How can there be a 500 error only when through a domain?

Question

PHP

The crux of the matter is that when you go to the admin panel (WP, ModX, Joomla 3) through the domain, a server error 500 appears (when adding materials or uploading files to the server), but when you go through the IP of the server where the site is located, miraculously all the errors disappear. There is nothing in the error logs, just empty no matter what I do. And through IP everything is fine. It seems that everything would be fine, but only there is a site where there are several sites on one server, and accordingly it is impossible to enter the admin panel via IP. What could be the problem? And yes, the problem appeared on 4 servers in one day.