Got error 502, 504 or whatever, forum is not loading and die after timeout, in our case the problem was in big cache file which fetches all core_acp_notifications from database... 

Just deleted all notifications and forum runs like F1, ok after redis like F1.. Maybe this would help someone save hours/days... Thanks...

Please check the System Logs for errors. More than likely there are a lot of errors you are being alerted to which need resolving. These could be from third party add-ons or something else. If you require further assistance, please update the access details in the Client Area so we can take a further look.