All forums gone

Hi,
i just realized that all forums are gone.
They are not displayed in the frontend nor in the backend.
https://jeroch-verlag.de/screens/asgaros3.jpg
But the tables are still in the database:
https://jeroch-verlag.de/screens/asgaros.jpg
https://jeroch-verlag.de/screens/asgaros2.jpg

– I have no idea how that happened.
– I have no idea how to solve it.

Can you please help?

Kind regards
Marcus

PS: actually i did this:
– added a new forum
– swaping the forum ids (old –>new)

(Thats why it seems as if it working)

But i fear that there will be problems following.
Or is it the right way?