This has happened a number of times with my UMO+ now. It started after I have brought a new hot end and temperature gauge.
I have tested the same file multiple times and it stops in a different place each time, I have even tried different files on a new SD card. When it stops the extruder head remains in the same place (doesn't return to home) and the bed lowers, making me think it could be a power supply issue rather than G-code related. I also print using a SD card.
Any help would be greatly appreciated.