I did a bit of an explainer in the CS lounge and a few other threads about what I THINK is going on. [CS Lounge] A New Year! 20-Years of WoW! - #1135 by Mirasol-mannoroth
The WoW forums treat each charname-server as a separate forum account. Separate trust level, flags, likes, ignore, etc. Earning TL3 requires maintaining a set number of days visited, posts read, a few likes given, and no suspensions.
There were a group of people who were put into a Battlenet level Beta group to allow posting of images and video on one of the Beta forums. That was granting Permanent TL3 to the whole account across all chars that did not decay or get removed if they were suspended on the forums. That was not intended.
I believe that got fixed.
Those that have otherwise earned it on a char should see it return on that char once the forums do their daily? update on trust levels. It does not do it in real time. There is a push once or twice a day for that update.
If they have a forum suspension on their account then they can earn it back starting 6 months after it expires.
So, that is what is going on. Some people who had permanent TL3 were not aware and are now confused as to why they lost it.