May not at all be related to your problem, but I’ve noticed big temperature changes in the shop can affect the belts.
I was running a long job last week-
and noticed a change in depth after about 5-10 minutes of running.
I’m pretty sure I didn’t loose steps, because it’s usually a pretty noticeable click.
But it was early and cold outside.
After that it didn’t change the rest of the day. Plus the machine is new with new belts. I’m thinking being brand new it might have a little stretching and breaking in to do, plus the temps going up and down would affect things a little. Not an 1/8" tho.