After rereading the post this solution worked for us as well :
For my case the problem was the permalink of User Groups page
If you go in the buddypress menu and the page menu.
In the User Groups section, check what is the selected page. After that, go in the page menu of wordpress and check the permalink of this page.
My problem was
https://bla-bla-bla/groups-2
It must be for the plugin group document to work correctly
https://bla-bla-bla/groups
But we still have a problem with the categories that are not saved when uploading a new doc.
Thanks for any help or redirection
