I have been having issue with my Shapeoko not holding its Z? I recently got new proximity switches and replace the old ones. I was making a Charcuterie board with several different pockets, towards the middle of the project the machine started pocketing about 1/4 inch above the stock then !/2 inch. I resarted and tried again and its the same thing. I’m currently only having issues when trying to use the pocket featured. So far it does the contour cuts good. What might be causing this
Sounds like you are loosing step on down-travel. That makes wiring issues unlikely, so focus on physical causes. What Z do you have? You could have something on the bearing rails, or even something that has travelled into the bearings, or maybe it just needs lubrication.
Another thing that could be is your bit is not tight and being pushed up. @mhotchin could also be right about losing steps. If the wood is very hard and too aggressive F&S that could cause the loss of steps.
If it is the bit being pushed up be sure with a Makita/C3D router you do the initial tightening with the lock button but the final tightening should be done with two wrenches. To eliminate that put a black magic marker at the bit where it goes into the collet. That would be a good visual indicator if the bit is loose and being pushed up.