After a few hours of usage , one of the first stage feeders does no longer pull the filament in. The filament is recognized when inserted, and the gear is audible But there is no force that pulls the filament into the feeder. The feeder is not clogged, because the filament can be inserted manually easily.
I had the same issue. The problem is that the gears of the feeders slip on the shaft because production managed to use thin oil/grease which creeped between shaft and gears.
How did I solve it?
Removed the gears from the shaft
Clean the oil/grease from the shaft and inside the gears