Recurring 404 error for all pages (but not posts or bbPress topics)

I have been tearing my hair out trying to solve an infuriating bug for the past few weeks, and after gathering as much info about this demon-bug as I can, I’m appealing to any higher powers in this forum to help me squash this. Please help…

The problem:

• Every 1-2 days, Pages of my WordPress site throw a 404 error.
• This seems to affect most/all Pages, but not Posts or forum Topics.
• The homepage, which I understand is also a Page, however, loads fine.
• So far I have been unable to reproduce the issue on demand, but it has been reliably cropping up every 1-2 days as mentioned.

Temporary solution: This seems to be temporarily resolved by simply clicking to Settings > Permalinks. I don’t need to actually DO anything at the permalinks settings menu, it seems that just clicking to it is somehow enough. However, the 404 errors come back again after 1-2 days.

Solutions researched / tried so far:

• Google searches usually suggest .htaccess edits, but I’m on an Nginx server so I’m not sure if .htaccess solutions are still relevant since Nginx supposedly doesn’t use them…?
• Googling permalinks nginx issues suggests to modify Nginx try_files to try_files $uri $uri/ /index.php?$args;, e.g. solution #2 here. I have tried this, but it does not seem to help.
• Disabling and enabling plugins does not seem to work, although I’m finding it difficult to definitively debug as I have to wait 1-2 days for the issue to crop up.

Possible relevant information:

Server setup: Linux [Ubuntu 20.04] + Nginx [1.18.0] + Mariadb [10.3.25] + PHP [7.4.3]

I’m using the Post Name permalink structure for my posts, e.g. https://DOMAIN.com/sample-post/

My .htaccess is as follows:

# BEGIN WP Rocket v3.8.3
# Use UTF-8 encoding for anything served text/plain or text/html
AddDefaultCharset UTF-8
# Force UTF-8 for a number of file formats
<IfModule mod_mime.c>
AddCharset UTF-8 .atom .css .js .json .rss .vtt .xml
</IfModule>
# FileETag None is not enough for every server.
<IfModule mod_headers.c>
Header unset ETag
</IfModule>
# Since we’re sending far-future expires, we don’t need ETags for static content.
# developer.yahoo.com/performance/rules.html#etags
FileETag None
<IfModule mod_alias.c>
<FilesMatch "\.(html|htm|rtf|rtx|txt|xsd|xsl|xml)$">
<IfModule mod_headers.c>
Header set X-Powered-By "WP Rocket/3.8.3"
Header unset Pragma
Header append Cache-Control "public"
Header unset Last-Modified
</IfModule>
</FilesMatch>
<FilesMatch "\.(css|htc|js|asf|asx|wax|wmv|wmx|avi|bmp|class|divx|doc|docx|eot|exe|gif|gz|gzip|ico|jpg|jpeg|jpe|json|mdb|mid|midi|mov|qt|mp3|m4a|mp4|m4v|mpeg|mpg|mpe|mpp|otf|odb|odc|odf|odg|odp|ods|odt|ogg|pdf|png|pot|pps|ppt|pptx|ra|ram|svg|svgz|swf|tar|tif|tiff|ttf|ttc|wav|wma|wri|xla|xls|xlsx|xlt|xlw|zip)$">
<IfModule mod_headers.c>
Header unset Pragma
Header append Cache-Control "public"
</IfModule>
</FilesMatch>
</IfModule>
# Expires headers (for better cache control)
<IfModule mod_expires.c>
	ExpiresActive on
	ExpiresDefault                              "access plus 1 month"
	# cache.appcache needs re-requests in FF 3.6 (thanks Remy ~Introducing HTML5)
	ExpiresByType text/cache-manifest           "access plus 0 seconds"
	# Your document html
	ExpiresByType text/html                     "access plus 0 seconds"
	# Data
	ExpiresByType text/xml                      "access plus 0 seconds"
	ExpiresByType application/xml               "access plus 0 seconds"
	ExpiresByType application/json              "access plus 0 seconds"
	# Feed
	ExpiresByType application/rss+xml           "access plus 1 hour"
	ExpiresByType application/atom+xml          "access plus 1 hour"
	# Favicon (cannot be renamed)
	ExpiresByType image/x-icon                  "access plus 1 week"
	# Media: images, video, audio
	ExpiresByType image/gif                     "access plus 4 months"
	ExpiresByType image/png                     "access plus 4 months"
	ExpiresByType image/jpeg                    "access plus 4 months"
	ExpiresByType image/webp                    "access plus 4 months"
	ExpiresByType video/ogg                     "access plus 4 months"
	ExpiresByType audio/ogg                     "access plus 4 months"
	ExpiresByType video/mp4                     "access plus 4 months"
	ExpiresByType video/webm                    "access plus 4 months"
	# HTC files  (css3pie)
	ExpiresByType text/x-component              "access plus 1 month"
	# Webfonts
	ExpiresByType font/ttf                      "access plus 4 months"
	ExpiresByType font/otf                      "access plus 4 months"
	ExpiresByType font/woff                     "access plus 4 months"
	ExpiresByType font/woff2                    "access plus 4 months"
	ExpiresByType image/svg+xml                 "access plus 1 month"
	ExpiresByType application/vnd.ms-fontobject "access plus 1 month"
	# CSS and JavaScript
	ExpiresByType text/css                      "access plus 1 year"
	ExpiresByType application/javascript        "access plus 1 year"
</IfModule>
# Gzip compression
<IfModule mod_deflate.c>
# Active compression
SetOutputFilter DEFLATE
# Force deflate for mangled headers
<IfModule mod_setenvif.c>
<IfModule mod_headers.c>
SetEnvIfNoCase ^(Accept-EncodXng|X-cept-Encoding|X{15}|~{15}|-{15})$ ^((gzip|deflate)\s*,?\s*)+|[X~-]{4,13}$ HAVE_Accept-Encoding
RequestHeader append Accept-Encoding "gzip,deflate" env=HAVE_Accept-Encoding
# Don’t compress images and other uncompressible content
SetEnvIfNoCase Request_URI \
\.(?:gif|jpe?g|png|rar|zip|exe|flv|mov|wma|mp3|avi|swf|mp?g|mp4|webm|webp|pdf)$ no-gzip dont-vary
</IfModule>
</IfModule>
# Compress all output labeled with one of the following MIME-types
<IfModule mod_filter.c>
AddOutputFilterByType DEFLATE application/atom+xml \
		                          application/javascript \
		                          application/json \
		                          application/rss+xml \
		                          application/vnd.ms-fontobject \
		                          application/x-font-ttf \
		                          application/xhtml+xml \
		                          application/xml \
		                          font/opentype \
		                          image/svg+xml \
		                          image/x-icon \
		                          text/css \
		                          text/html \
		                          text/plain \
		                          text/x-component \
		                          text/xml
</IfModule>
<IfModule mod_headers.c>
Header append Vary: Accept-Encoding
</IfModule>
</IfModule>
# END WP Rocket
RewriteEngine On 
RewriteCond %{HTTPS} off 
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
# BEGIN WordPress
# The directives (lines) between "BEGIN WordPress" and "END WordPress" are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress
# php -- BEGIN cPanel-generated handler, do not edit
# Set the “ea-php74” package as the default “PHP” programming language.
<IfModule mime_module>
  AddHandler application/x-httpd-ea-php74 .php .php7 .phtml
</IfModule>
# php -- END cPanel-generated handler, do not edit
# BEGIN cPanel-generated php ini directives, do not edit
# Manual editing of this file may result in unexpected behavior.
# To make changes to this file, use the cPanel MultiPHP INI Editor (Home >> Software >> MultiPHP INI Editor)
# For more information, read our documentation (https://go.cpanel.net/EA4ModifyINI)
<IfModule php7_module>
   php_flag display_errors Off
   php_value max_execution_time 30
   php_value max_input_time 60
   php_value max_input_vars 1000
   php_value memory_limit 512M
   php_value post_max_size 260M
   php_value session.gc_maxlifetime 1440
   php_value session.save_path "/var/cpanel/php/sessions/ea-php74"
   php_value upload_max_filesize 256M
   php_flag zlib.output_compression Off
</IfModule>
<IfModule lsapi_module>
   php_flag display_errors Off
   php_value max_execution_time 30
   php_value max_input_time 60
   php_value max_input_vars 1000
   php_value memory_limit 512M
   php_value post_max_size 260M
   php_value session.gc_maxlifetime 1440
   php_value session.save_path "/var/cpanel/php/sessions/ea-php74"
   php_value upload_max_filesize 256M
   php_flag zlib.output_compression Off
</IfModule>
# END cPanel-generated php ini directives, do not edit
Options -Indexes

In my server, /etc/nginx/sites-enabled/300h.conf yields:

server {
    server_name go.DOMAIN.com DOMAIN.com www.DOMAIN.com;

    root /var/www/html;
    index index.php;
    charset UTF-8;

    client_max_body_size 128m;

    ##
    # gzip config
    ##
add_header Strict-Transport-Security "max-age=31536000";

brotli on;
brotli_comp_level 6;
brotli_types text/xml image/svg+xml application/x-font-ttf image/vnd.microsoft.icon application/x-font-opentype application/json font/eot application/vnd.ms-fontobject application/javascript font/otf application/xml application/xhtml+xml text/javascript  application/x-javascript text/plain application/x-font-truetype application/xml+rss image/x-icon font/opentype text/css image/x-win-bitmap;

#  if ($http_host = "ask.DOMAIN.com") {
#      rewrite ^ https://forum.DOMAIN.com permanent;
#   }

#  if ($http_host = "forum.DOMAIN.com") {
#     rewrite ^/(.*)$^ https://DOMAIN.com/forum/$1 permanent;
# }

#Yoast SEO Sitemaps

location ~ ([^/]*)sitemap(.*).x(m|s)l$ {

  ## this rewrites sitemap.xml to /sitemap_index.xml

  rewrite ^/sitemap.xml$ /sitemap_index.xml permanent;

  ## this makes the XML sitemaps work

  rewrite ^/([a-z]+)?-?sitemap.xsl$ /index.php?yoast-sitemap-xsl=$1 last;

  rewrite ^/sitemap_index.xml$ /index.php?sitemap=1 last;

  rewrite ^/([^/]+?)-sitemap([0-9]+)?.xml$ /index.php?sitemap=$1&sitemap_n=$2 last;

  ## The following lines are optional for the premium extensions

  ## News SEO

  rewrite ^/news-sitemap.xml$ /index.php?sitemap=wpseo_news last;

  ## Local SEO

  rewrite ^/locations.kml$ /index.php?sitemap=wpseo_local_kml last;

  rewrite ^/geo-sitemap.xml$ /index.php?sitemap=wpseo_local last;

  ## Video SEO

  rewrite ^/video-sitemap.xsl$ /index.php?yoast-sitemap-xsl=video last;

}
    gzip on;
    gzip_static on;
    gzip_vary on;
    gzip_disable "msie6";
    gzip_types text/css text/x-component application/x-javascript application/javascript text/javascript text/x-js text/richtext image/svg+xml text/plain text/xsd text/xsl text/xml image/x-icon;
    gzip_http_version 1.1;
    gzip_comp_level 6;
    gzip_proxied any;

    ##
    # Server log config
    ##

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log warn;

    ##
    # FastCGI cache exceptions
    ##

    set $no_cache   0;
    set $cache_uri  $request_uri;

    if ($request_method = POST) {
        set $cache_uri  "null cache";
        set $no_cache   1;
    }

    if ($query_string != "") {
        set $cache_uri  "null cache";
        set $no_cache   1;
    }

    if ($request_uri ~* "(/wp-admin/|/xmlrpc.php|/wp-(app|cron|login|register|mail).php|wp-.*.php|/feed/|index.php|wp-comments-popup.php|wp-links-opml.php|wp-locations.php|sitemap(_index)?.xml|[a-z0-9_-]+-sitemap([0-9]+)?.xml)") {
        set $cache_uri  "null cache";
        set $no_cache   1;
    }

    if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_logged_in") {
        set $cache_uri  "null cache";
        set $no_cache   1;
    }

    ##
    # Browser cache config
    ##

    location ~ \.(css|htc|js|js2|js3|js4)$ {
        expires max;
        add_header Pragma "public";
        add_header Cache-Control "max-age=31536000, public, must-revalidate, proxy-revalidate";
    }

    location ~ \.(html|htm|rtf|rtx|svgz|txt|xsd|xsl|xml)$ {
        try_files $uri $uri/ /index.php?q=$uri&$args;
        
        expires 3600s;
        add_header Pragma "public";
        add_header Cache-Control "max-age=3600, public, must-revalidate, proxy-revalidate";
    }

    location ~ \.(webp|woff2|woff|asf|asx|wax|svg|wmv|wmx|avi|bmp|class|divx|doc|docx|eot|exe|gif|gz|gzip|ico|jpg|jpeg|jpe|json|mdb|mid|midi|mov|qt|mp3|m4a|mp4|m4v|mpeg|mpg|mpe|mpp|otf|odb|odc|odf|odg|odp|ods|odt|ogg|pdf|png|pot|pps|ppt|pptx|ra|ram|svg|svgz|swf|tar|tif|tiff|ttf|ttc|wav|wma|wri|xla|xls|xlsx|xlt|xlw|zip)$ {
        expires max;
        add_header Pragma "public";
        add_header Cache-Control "max-age=31536000, public, must-revalidate, proxy-revalidate";
        log_not_found off;
    }

    ##
    # Favicon
    ##

    location = /favicon.ico {
        log_not_found off;
        access_log off;
    }

    ##
    # robots.txt
    ##

    location = /robots.txt {
        allow all;
        log_not_found off;
        access_log off;
    }

    ##
    # Deny access to hidden files
    ##

    location ~ /\. {
        deny all;
    }

    ##
    # Deny access to uploaded PHP files
    ##
    #
    location ~* /(?:uploads|files)/.*\.php$ {
        deny all;
    }

    ##
    # Deny access to WordPress include-only files
    ##

    location ~ ^/wp-admin/includes/ {
        deny all;
    }
    location ~ ^/wp-includes/[^/]+\.php$ {
        deny all;
    }
    location ~ ^/wp-includes/js/tinymce/langs/.+\.php {
        deny all;
    }
    location ~ ^/wp-includes/theme-compat/ {
        deny all;
    }

    location / {
#        try_files $uri $uri/ /index.php?q=$uri&$args;
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ \.php$ {
        try_files $uri =404;

        include fastcgi_params;
        fastcgi_param  SCRIPT_FILENAME    $document_root$fastcgi_script_name;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_index index.php;
        # fastcgi_intercept_errors on;
        # fastcgi_keep_conn on;
        # fastcgi_read_timeout 300;

        # fastcgi_pass   127.0.0.1:9000;
        fastcgi_pass  unix:run/php/php7.4-fpm.sock;

        ##
        # FastCGI cache config
        ##

        # fastcgi_cache_path /var/cache/nginx levels=1:2 keys_zone=WORDPRESS:10m max_size=1000m inactive=60m;
        # fastcgi_cache_key $scheme$host$request_uri$request_method;
        # fastcgi_cache_use_stale updating error timeout invalid_header http_500;
  #      fastcgi_no_cache $no_cache;
 #       fastcgi_cache_bypass $no_cache;
#        fastcgi_cache WORDPRESS;
#fastcgi_cache_valid any 30m;
    }

    listen 443 ssl http2; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/DOMAIN.com-0001/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/DOMAIN.com-0001/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}
server {
    server_name ask.DOMAIN.com;
    return 301 https://DOMAIN.com/forum$request_uri;

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/DOMAIN.com-0001/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/DOMAIN.com-0001/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server {
    server_name forum.DOMAIN.com;
    return 301 https://DOMAIN.com/forum$request_uri;

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/DOMAIN.com-0001/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/DOMAIN.com-0001/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

server {
    if ($host = www.DOMAIN.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    if ($host = go.DOMAIN.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    if ($host = DOMAIN.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    listen 80;
    server_name go.DOMAIN.com DOMAIN.com www.DOMAIN.com;
    return 404; # managed by Certbot

}
server {
    if ($host = ask.DOMAIN.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    listen 80;
    server_name ask.DOMAIN.com;
    return 404; # managed by Certbot

}

server {
    if ($host = forum.DOMAIN.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    listen 80;
    server_name forum.DOMAIN.com;
    return 404; # managed by Certbot

}

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