Given the symptoms and what you did to ‘correct’ it, I’d guess at a wiring short/break in your harness for that axis. I built a Delta printer a couple of years ago and I hand wired and soldered all of the cabling for the motors and had a similar sounding issue with the extruder motor. It would shake and shudder, sometime going to opposite way. No seeming rhyme or reason. Upon closer inspection I found a bad wire in one of my sleeved connections. Fixed and it was fine. Try moving the axis over a long distance while fiddling with the wiring to see if you can make it misbehave. If so, you found your culprit.