I think I have the same problem. For me, the gcode for z doesn’t match the sled position for the z axis reported by webcontrol. Additionally, there was visible evidence when pocketing where the depth was not always the same and caused an uneven pocket, more profound with more z movements.
I did not find a perfect fix. However, I found that slowing down the plunge speed while creating the gcode reduced the error.
Here is a link to my post with what I think may be the same issue. Z axis depth different between Sled and Gcode