There are two different makers of the Official Arduino UNO. www.arduino.cc & www.arduino.org. We purchased an Arduino UNO from inventables and it was a Genuine Official one and it works flawlessly with the J-Tech LaserMode grbl firmware. It’s from Arduino.org. It’s the one that I have been using with my 6W LD/Flexmod P3 build.
Prior to that we were using the Genuine Official one purchased at Radio Shack from Arduino.cc and worked flawlessly with the J-Tech LaserMode grbl firmware also, There has been some confusion why the X-Carve’s UNO works for some, but not others.
All I can suggest is to try the J-Tech LaserMode grbl with your X-Carve first before changing out your UNO.
In grbl 9g it has a setting $14=1 (auto start, bool) where grbl 9i + does not, so make sure this is set to 1 not 0, or nothing will move.