Possibly caused by backlash. You can try balancing the mount so it is east-heavy. This will load the gears and take up the slack in RA. See
this explanation for example.
If unsure how to do it, balance the RA axis well, pick an object in the west and shift the counterweight a bit one way. Take an image which shows the star jump, shift the counterweight the other way (from the balanced position) and try imaging again. See if that helps.
If it works, note that the counterweight must be shifted the other way once you go back to the east side of the sky.