I was cutting a pocket in acrylic on my XL (bought 11/16) when about 20 minutes in it suddenly started cutting through the acrylic and several mm into the wasteboard. Originally the Z zero was paper thickness above the stock, but after I canceled the job, zero was about 13.5 mm below where it was originally set. There were no retractions or other upward movements at the time. I would expect skipped steps or a slipped pulley to cause it to cut too high, rather than too low. A false trigger on Z home would cause it to try plunging 80mm below the original position. On the piece that was inadvertently cut out, I can see an edge where it ramped down to the new mistaken depth. It wasn’t a sudden plunge.
Could this be a bug with Carbide Motion, or is there something else that could cause Z to change to below the stock? A slipping pulley could do it on retraction, but there were no travel moves in the section were the error occurred.