Having the V-wheels too tight can cause problems too. Right now I can move the V-wheels by hand if I really try hard, and it made everything a bit better. If it’s too tight, then it may be putting extra torque on the stepper motor since the bearings are far from frictionless.
Check out this forum post for some good pot information: New drifting
As for the loose pulleys, it’s very possible for the little screws to come loose (or even come out). If that happens, it can cause the shaft to spin in the pulley without actually turning the pulley. Double check that they are tight, and throw some loc-tite in them as well if you notice they start to loosen up. Mine are still solid, but the first time one loosens up they’re all getting locked.