I've got a TB6600 stepper motor driver connected via a common cathode connection to an Arduino (Elegoo) Nano microcontroller (1/32 microsteps, 1.5A, unknown NEMA 17). I'm asking it to move a number of steps, but every so often it will move way too far (at roughly the same speed, so it moves for a much longer period of time). The problem is intermittent, and it seems to go away when I have probes attached.
I really can't think of any scenario which would cause overstepping like this. What might be causing it?
I've checked that the microcontroller is outputting the right number of steps.