On my Totem I recently had an output where half of the output were shifted some mm in Y. It looked like a classical jumped tooth on the belt, e.g. from hitting the frame.
But, when I told it to move to my reference point (the Totem has no endstops) directly after, it hit it spot on. No shift at all. So unless it jumped one tooth in Y+ and then later one tooth in Y- (and that on both belts at the same time, the output was not crooked), It doesn’t seem to be a mechanical issue.
I ran the file again and the result was fine, so I’m not too concerned about it. But it still irks me that I don’t know what happened there…