When I upgraded the new stable cPanel for some reason and I can't find out how to fix it.
cubicwebs.com/cpanel and cubicwebs.com/whm both go to a 500 internal error page instead of redirecting to the control panel login.
It's frustrating my clients and I have numerous support tickets about it, I've looked everywhere and nothing has changed.
This is actually related to your litespeed which we do not support. You will need to ensure that it is working correctly to access your server. In the meantime you can see that it is not a cPanel issue because you can access your server via IP/whm or IP/cpanel without any issues.