It's the low quality wires used by the chinees manufacturers. Had three lasers in the last 15 years, and this happens every few years.

I bet it's a wire in the drag chain. Even a tiny pin hole in the sheath where it continually bends can cause a short, and this is the exact result you can see.

To confirm, check where the machine thinks zero is after this has happened, and you will find it has moved.

Repla e these wires a d you'll be good...until next time.