Solved Pagination doesn't work

Also, I tried the statistics recount in Kunena Tools, and did all the database tools in CB, cleared cache, and tried again, but still the same

A few things I tried:
- Tried to create a new Kunena Category menu item, used that to load the forums and tried again, same result

I checked your menus. The sort of the menu items are not correct.
Example:
The menu item 1504 Forum linked to the defaultmenu=1505 and target is forum/index
The menu item 1513 Forum linked also to the defaultmenu=1505 but the targed is forumnl
You can't use sundry targets with the same menu ID.
But that's only a single example. You have more then one menu items with the same target, but different address.
You must repair the menu items, otherwise remain the problem.

I have corrected this now:

form -> id 1505
forumnl -> 1514

So now, for each language there is a different menu item for Kunena. Which is indeed a good thing.

But unfortunately, this still has not resolved the problem

Update: I have found the cause of the issue!

It was a module called "Article Module" (which places an article inside a module). When I don't publish that module on pages of Kunena, the pagination works again!