Had a similar problem on a stepper motor motion control system in a vacuum chamber. The single electrical feedthrough forced motor and signal cables to be in close proximity. The pwm noise from the motors would couple to the opto isolated limit switch signal and force the limit switches on. I solved it by putting 10k pull down resistors with a bypass capacitor to ground on all the inputs. Phantom stuck limits were no more.
I’ve found recently that ferrites really help with this. The electrical noise from large steppers is really erratic, but responds well to ferrite beads with 2-3 wraps. I put one at each end of the cable, since back-EMF is very real in large steppers.
