I've had the logging issue with Facebook in recent days. All the users came from Facebook --> went to Xenforo via the link in Facebook -->tried to log in --> Logged in and then were pushed to log out again and again.
Thank you for your feedback. Some our users reported this issue to me. And I had faced it at the previous time of disabling all ad-ons as well. So I think I will observe it in the next couple of days.