This makes me think of a problem the Yamaha IT forum was having before it closed down. That being, not being able to log on, then some being able to log on and others not being able to. I don't think there was ever a reason given or discovered.
As I mentioned in an earlier comment, I only received the banned message once. The wording ('You've been banned') made me suspicious that the sight had been hacked.
If it helps, I don't allow third party trackers on my laptop and also clear my cookie cache regularly. Maybe that helped my situation...or maybe not.
Hope you get it sorted soon.