If you run a CodeIgniter site on Cloudways hosting you may come across this problem. All the CodeIgniter sites on the server stop working and display the message: “File not found.” with a 404 response.
The problem is caused by Apache 2.4.10 updating to Apache 2.4.25 (PHP FPM and FastCGI).
The solution is to update the .htaccess file so that
RewriteRule ^(.*)$ /index.php/$1 [L]
RewriteRule ^(.*)$ /index.php?/$1 [L]
note the extra ? character after .php