I’m having what might be the same issue. Got my printer set up around Christmas time, and it was doing small prints fine. It STILL does small prints fine. The longer it runs, the more likely it is to have the motors jerk and cause x/y layer shifts. I have watched everything on the machine fastidiously when it happens. The tracks are smooth, everything seems tensioned right, the spool isn’t the problem. What could cause this? Electronics getting hot? Grounding issues?