More often than not when importing from vbulletin it's a good idea to start over with permissions. And definitely make sure Regisered is primary group for all users, and any other groups are all secondary.
So you might have registered set with whatever the base permissions should be. Maybe needing moderation, but then have a promotion so that anyone with x posts (in my case one is fine) gets promoted to a group who has permission to post with moderation.
Or however you want to do it.
End-user documentation for XenForo
(it's different to vbulletin)