mod_rewrite frustration

My mod_rewrites were working well until a few months ago, when they seemed to spontaneously break. ;(

https://mysite.com/musica.php?item=54 displays the page as I would like.

I’d like to be able to enter https://mysite.com/musica.php/media/test/54 and get the same page. However, when I use the following mod_rewrite, I get a 404 error:

RewriteRule ^musica.php/media/([^/\.]+)/([^/\.]+) /musica.php?item=$2 [QSA,L]

When I do a 301 redirect instead, it works fine, suggesting it’s not a problem with the regular expression:

RewriteRule ^musica.php/media/([^/\.]+)/([^/\.]+) /musica.php?item=$2 [R=301,L]

Any ideas? For the sake of completeness, here’s the code in my functions.php I’m using to generate these rewrites:

add_action('generate_rewrite_rules', 'wp_insertMyRewriteRules');
add_action('admin_init', 'my_flush_rules');

function my_flush_rules(){
    global $wp_rewrite;
    $wp_rewrite->flush_rules();
}

function wp_insertMyRewriteRules($rules) {
        global $wp_rewrite;
	$newrules = array();
	$newrules['musica.php/media/([^/\.]+)/([^/\.]+)'] = 'musica.php?item=$2';
        $wp_rewrite->non_wp_rules = $newrules + $wp_rewrite->non_wp_rules;
}

and here’s an abbreviated copy of my .htaccess file:

<IfModule mod_rewrite.c>
RewriteRule ^category/(.+)$ https://mysite.com/ [R=301,L]
RewriteRule ^tag/(.+)$ https://mysite.com/ [R=301,L]
RewriteRule ^postings$ https://mysite.com/ [R=301,L]
</IfModule>

# BEGIN W3TC Page Cache core
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteBase /
    RewriteCond %{HTTP:Accept-Encoding} gzip
    RewriteRule .* - [E=W3TC_ENC:_gzip]
    RewriteCond %{REQUEST_METHOD} !=POST
    RewriteCond %{QUERY_STRING} =""
    RewriteCond %{HTTP_COOKIE} !(comment_author|wp-postpass|w3tc_logged_out|wordpress_logged_in) [NC]
    RewriteCond "%{DOCUMENT_ROOT}/wp-content/cache/page_enhanced/%{HTTP_HOST}/%{REQUEST_URI}/_index.html%{ENV:W3TC_ENC}" -f
    RewriteRule .* "/wp-content/cache/page_enhanced/%{HTTP_HOST}/%{REQUEST_URI}/_index.html%{ENV:W3TC_ENC}" [L]
</IfModule>
# END W3TC Page Cache core

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteRule ^musica.php/media/([^/\.]+)/([^/\.]+) /musica.php?item=$2 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

IndexIgnore *

Thanks so much for your help!