Looking at the photo - things aren't right, are they!?
I'd be looking at what spacers are fitted between the brakeplate and the sprocket (is there sufficient clearance?), and especially what's going on between the flange on the stub-axle and the bearing in the drum, and if the bearing's still correctly seated in the drum - i.e. is the circlip still holding the bearing in place?
If the circlip springs out the drum can 'walk around' on the bearing, which would let it walk away from the cush drive. The NOC notes mention that the circlip needs to be fitted with the sharp edges away from the bearing. Ask me how I know
It certainly needs pulling down for inspection