When I set the velocity to 45 the motor hops around. It's back and forth all over the place.
At 100 the motor runs smooth.
At first glance, that sounds like resonance. It can be a real pain.
Simple (cheaper) drivers cannot handle this. You need a fairly sophisticated driver to do so. It can take a significant amount of processing power to suppress the resonance.
You MIGHT be able to reduce the effect by adding a 'damper'. A solid disk on the motor shaft, coupled to the shaft via something very lossy might help. Plasticene, Blu-Tack, double-sided foam tape, are all possibles. None of them last very well though.
Cheers
Roger