I was having a similar problem, the machine stops in the middle of the carve about 50% of the time. Possible causes I considered:
- UGCS, 2. USB to PC cable problem (cable was older and long), 3. PC problem, 4. X-Carve problem (X-controller upgrade WAS incorporated), 5. 115 VAC problem (vacuum and X-carve are on the same circuit, possibly introducing noise). Cheap and easy things first.
Replaced the USB cable with a shorter new cable. On the PC, made sure that it’s not doing anything else. That is, has open browser windows, mail, or any other things that might generate an interrupt that caused UGCS to glitch. I had purchased PIC sender and had it in reserve to eliminate UGCS but did not use.
Result of only replacing the USB cable and off-loading the PC was that I haven’t seen any stopages yet. Can’t say that I have THAT many hours to verify fix. Can’t prove, but if you don’t have the X-controller upgrade, I would guess that you could have noise on wiring to the Arduino. I had some problems with the Arduino version when I first tried to get the Z cal mode to work. Fix was to do a better job with signal grounding. Good luck.