Nginx error log will indicate errors such as the following:
nginx: [emerg] too long parameter "#### SSL P..." started in /etc/nginx/conf.d/users/username.conf:50
nginx: configuration file /etc/nginx/nginx.conf test failed
This issue can break users nginx configurations. The issue is how long the list of SSL proxied domains is. Nginx has a hard coded limit and can be broken on accounts with a large number of domains. We do have an open case with our developers to look into increasing the buffer value to accomate accounts with a large number of domains. The case ID is CPANEL-37343.
The current work around is to delete the referenced line from the file. The line would be readded if any further domains are added to the account, or new SSLs are installed or removed.