Hello
I can help you to debug your server issue/s and update your htaccess file and rewrite rules. I have over 20 years extensive experience with Apache and its modules, including the mod_rewrite module and have completed many projects with issues similar to yours, over many years.
If you would like to send through some additional information on your server set up, including a copy of your htaccess file the way it is now, some example URLs that you are having issues with, as well as what version of Apache and Server (OS) you are running, I can review it and confirm back with you.
I can also clean up and optimise the code where required to ensure your site runs as a high performance server, with specific custom developed directives that can speed up your site performance up to 30% faster on some requests.
Thank you
Darren