If you attach a serial console (the micro-B USB cable would allow a host PC to use serial console) and run “dmesg --follow”, and enable a log with the serial console, what do you see near the end of the log in cases where it shuts down?
FYI, I prefer “gtkterm” for a serial console, e.g., “sudo apt-get install gtkterm”. If on the host PC you monitor “dmesg --follow”, and then connect the provided micro-B USB cable to the Xavier and the full-sized type-A to the host PC, you will see four ttyUSB# show up. The last one should be the serial console. So if for example the last one is “ttyUSB8”, serial console with gtkterm would go like this:
gtkterm -b 8 -t 1 -s 115200 -p /dev/ttyUSB8
# Then in the terminal:
# Now turn on logging.
If the Xavier reboots, post the content of the log. You might need to name the log with a “.txt” file suffix. If you hover your mouse over the quote icon in the upper right of an existing post, then other icons will show up. The paper clip icon will allow attaching the log file.