custom 404 page keeps getting trashed

Hello, as title says. after few days i setup the custom page, it gets trashed. right now only compatibility mode is active (avada theme) because it won’t load correctly.i also tried enabling the option that sends error 404 if the page is accessed directly. same result.this happens to all 4 sites i installed it

system status

### WordPress ###

Home URL: https://delphicomunicazione.it
Site URL: https://delphicomunicazione.it
WordPress Version: 5.3.2 ?
WordPress Multisite: No
WordPress Memory Limit: 40M
WordPress Debug Mode: No
WordPress Debug Log: No
WordPress Script Debug Mode: No
WordPress Cron: Yes
WordPress Alternate Cron: No
Background tasks: No ? cURL error 28: Operation timed out after 2001 milliseconds with 0 bytes received

### Active Theme ###

Avada: by ThemeFusion (https://themeforest.net/user/ThemeFusion) – 6.1.2 ?

### Active Plugins ###

404page – your smart custom 404 error page: by Peter Raschendorfer – 11.2.1 ?
Akismet Anti-Spam: by Automattic – 4.1.3 ?
Better Search Replace: by Delicious Brains – 1.3.3 ?
Buttonizer – Smart Floating Action Button (Premium): by Buttonizer – 2.0.8 ?
Column Shortcodes: by Codepress – 1.0 ?
Coming Soon Page, Under Construction & Maintenance Mode by SeedProd: by SeedProd – 5.1.0 ?
Companion Auto Update: by Papin Schipper – 3.4.8 ?
Contact Form 7: by Takayuki Miyoshi – 5.1.6 ?
Cookie and Consent Solution for the GDPR & ePrivacy: by iubenda – 2.0.2 ?
Duplicate Page: by mndpsingh287 – 4.0 ?
Duplicate Post Page Menu & Custom Post Type: by Inqsys Technology – 1.4.2 ?
Easy FancyBox: by RavanH – 1.8.18 ?
Easy Social Icons: by cybernetikz – 3.0.7 ?
Email Templates: by Damian Logghe – 1.3.1.2 ?
Flamingo: by Takayuki Miyoshi – 2.1.1 ?
Fusion Builder: by ThemeFusion – 2.1.2 ?
Fusion Core: by ThemeFusion – 4.1.2 ?
Google Analytics for WordPress by MonsterInsights: by MonsterInsights – 7.10.3 ?
Issuu PDF Sync: by Benjamin Niess – 3.1.2 ?
LayerSlider WP: by Kreatura Media – 6.10.0 ?
Magic Liquidizer Responsive Table: by Elvin D. – 2.0.4 ?
Official Facebook Pixel: by Facebook – 1.8.0 ?
OrganicWeb Read Only Gravity Forms: by Gary Eckstein – 0.1.0 ?
Postman SMTP: by Jason Hendriks – 1.7.2 ?
Public Post Preview: by Dominik Schilling – 2.9.0 ?
Public Post Preview Configurator: by Bj?rn Weinbrenner – 1.0.3 ?
Really Simple CAPTCHA: by Takayuki Miyoshi – 2.0.2 ?
Redirection: by John Godley – 4.6.2 ?
Remove Dashboard Access: by Drew Jaynes (DrewAPicture) – 1.1.3 ?
Responsive Flipbooks: by Peak Technologies Ltd. – 1.0 ?
Revisionize: by Jamie Chong – 2.3.2 ?
Search Exclude: by Roman Pronskiy – 1.2.5 ?
Shortcodes Ultimate: by Vladimir Anokhin – 5.6.2 ?
SiteOrigin CSS: by SiteOrigin – 1.2.4 ?
Sticky Menu (or Anything!) on Scroll: by Mark Senff – 2.1.1 ?
Symple Shortcodes: by AJ Clarke – 2.1.3 ?
TinyMCE Advanced: by Andrew Ozz – 5.3.0 ?
WP-MailUp: by MailUp and N. I. Biz Soft Solutions – 1.4.11 ?
WP-Sweep: by Lester ‘GaMerZ’ Chan – 1.1.1 ?
WP Booklet: by BinaryStash – 2.1.8 ?
wpDiscuz: by gVectors Team (A. Chakhoyan, G. Zakaryan, H. Martirosyan) – 5.3.5 ?
WPS Hide Login: by WPServeur, NicolasKulka, tabrisrp – 1.5.5 ?
Yoast SEO Premium: by Team Yoast – 12.7 ?

### Web Server ###

Software: Apache

### PHP ###

Version: 7.2.27 ?
Memory Limit: 512M
Maximum Execution Time: 299
Maximum File Upload Size: 128M
Maximum File Uploads: 20
Maximum Post Size: 128M
Maximum Input Variables: 8000
cURL Enabled: Yes (versione 7.55.0)
OpenSSL: OpenSSL 1.0.2k 26 Jan 2017 (268443839)
Mcrypt Enabled: No
Mbstring Enabled: Yes
Loaded Extensions: Core, date, libxml, openssl, pcre, zlib, bz2, calendar, ctype, hash, filter, ftp, gettext, gmp, SPL, iconv, pcntl, readline, Reflection, session, standard, SimpleXML, sockets, mbstring, tokenizer, xml, cgi-fcgi, mysqlnd, bcmath, curl, dba, dom, enchant, fileinfo, gd, imagick, imap, intl, json, ldap, exif, mysqli, odbc, PDO, pdo_mysql, PDO_ODBC, pdo_pgsql, pdo_sqlite, pgsql, Phar, posix, pspell, redis, soap, sodium, sqlite3, sysvmsg, sysvsem, sysvshm, tidy, xmlreader, xmlrpc, xmlwriter, xsl, zip, ionCube Loader, Zend OPcache

### MySQL ###

Version: 5.5.5 ?
Database Character Set: utf8
Database Collation: utf8_general_ci

### Date and Time ###

WordPress (Local) Timezone: Europe/Rome
MySQL (UTC): 2020-02-05 09:53:47
MySQL (Local): 5 Febbraio 2020 alle 10:53
PHP (UTC): 2020-02-05 09:53:47
PHP (Local): 5 Febbraio 2020 alle 10:53