As an old industrial maintenance man.
I have a lot experience with gates belts and bearings. The problem is the belt is tight and is loading the bearing. Do you see it with one of the bottom bracket more than the other?
There could be a small miss Alinement of the the two BB’s causing this issue. This can increase over over time as the pressure from the belt will increase the Alinement issue. If properly aligned the bearings and belt will last for years.