What could be causing a 404 error when trying to access PHP files with the number 5 in the filename?

The issue could be related to the server misinterpreting the number 5 in the filename as a parameter or variable, causing a 404 error. To solve this, you can try adding a RewriteRule in the .htaccess file to handle URLs with numbers in the filename correctly.

RewriteEngine On
RewriteRule ^(.*)5(.*)$ $1_5$2 [L]