Quote Originally Posted by cncartist View Post
If what you are experiencing is a true shift on half of your prints, I would suspect a tooth in the belt has worn or broken - it would be visible. I'd recommend to check the belts first and to diagnose which axis is shifting.
Seeing shifting on the Y axis, and the weird thing is, it is hit and miss. I can run the same print twice and not see it on the first print but then appears on the second.

Pulled the sides off and checked the teeth on the belt and on the pulleys, all seem to be good. I also made sure the grub screws were in place and none were missing.
Tightened the Y motor, even though the tension on the belt seemed good. While I had the machine apart, I used your guide to oil the bearings (TY for the guide BTW).

Running another print now to see if it made any difference.