I too experienced disconnect issues and have since been using an inexpensive powered USB hub bought from local store. Prior to that, I had good luck by bypassing the USB header and plugging a cord directly into the mini usb slot normally used by the header cable as a temporary fix. And, to diagnose if this was in fact my issue. For me, it was and have been happily carving without the intermittent disconnects.
For the cable, I found a spare USB cable normally used for charging my android phone. You will have to remove the face of the X-Controller and slide the lid back to reach the port. Be careful as you will be working around the E Stop button. In fact, I would suggest unplugging the X Controller first.
Disclaimer: I’m not suggesting this will fix your issue, but it may help you get to the root cause. If you want to avoid opening up the X Controller, just try the USB powered hub.
Here is a thread I found with a suggestion for a USB hub and cable: x-carve-randomly-crashes-and-loses-connection-power-issue-perhaps