Question Problems after updating to 5.2

When trying to post a quick answer to a topic, the console displays: GET www.people-abroad.de/forum/topic/ 404 (Not Found)

When trying to create a new topic, the console does not display any error message. Same happens when trying to post a regular (not quick) answer.

I found another 404 error in the console when opening an existing thread: GET www.people-abroad.de/forum/user/listmention.raw/ 404 (Not Found)
The thread does display fine, though.

Please check your Kunena menu items. Many errors come from wrong configured Kunena Menu items. I cannot see any logic in the paths.
The menu item "Übersicht" show the path .../forum/index/ but goes to the statistics 
The Index is called by this address .../forum/forum
See also here:

Hi,
I did a complete "trash-burn", i.e. deleted the Kunena menu, and related menu items from the main menu (and then emptied the trashcan). Used the "restore Kunena menu" option. Now the forum can be opened here: www.people-abroad.de/forum
However, the same problems are still there Somehow, this installation is broken it seems...

Please disable the jch optimize, then empty the cache and test again whether it's not possible to create a new topic.

Hi,
I disabled the JCH Optimize plugin, then deleted the cache. The problems are still there, though, with the same behavior.

Please, would you create an account for me? An account for the frontend (Registered user) would be enough. You can use the confidential tags for the access data (padlock symbol in the editor), then are this info visible only for you and moderators here.