I noticed that my zigbee2mqtt restarted more and more often this winter. In december it could be once in a week, but each day in the beginning of april.
Then one day I noticed that it restarted at the exact moment I opened the door to the closet my RPi is located. It even restarted when I was blowing air at the Sonoff coordinator 
So I exchanged the USB extension cable with a new one and it has not restarted a single time since then. (but I have probably jinxed it when writing about it)
Anyway, it is only my little story about it is not always the software that fails. Even a simple cable could be a problem.