2.9.0 b No permission for group admin after adding forum

[alfa1]

A member of my forum reports this issue:

I started social group 2728. Privacy is: Open and all posts moderated. I attempted to add a forum to the group. Now, I can't access the group at all. I get an error message saying that I don't have permission to view the page.

 

[alfa1]

probably the same as this:
https://nobita.me/threads/cannot-po...ve-insufficient-privileges-to-post-here.1634/