[Jon Stratis]

It sounds like there might be an issue with that particular Y cable. You said there weren't any visual strands poking out, but if the cable got crimped at some point, or if there was a manufacturing defect in the insulation when it was assembled, there could be someplace in the cable that is shorting out occasionally. It may be small enough that, when enabled, the PWM signal from the roboRIO is strong enough to mask it out, regardless of what value you're instructing the motor to go.

Try just replacing the Y cable, and if that works cut the other one in half* and toss it!


* Make it unusable so someone else on the team doesn't see it sitting on top of the trash and think "why is this being thrown out? I'll save us a buck and stick it in our spare parts drawer so we don't have to buy another one down the line."