Losing zero can be many things, most of them mechanical.
Here is something you can check to see if it’s a controller issue.
When you get ready to start a pass, after zeroing and all the setup, issue a $# command this will dump out the machine position for each of the work spaces. Most likely you are going to be using G54. Write down the machine position from the G54 (or other system if it’s the one you use). Then run your pass.
After the pass finishes, do the $# command again before you press “return to zero” and see if the machine position for G54 (or other) is the same as it was when you started the pass.
If G54 (or other) doesn’t change throughout your project, then the problem is most likely mechanical.
Also, take note of the command that UGCS sends when you press “return to zero”. Post this here. Also post the $G and $# output.
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