I had BackupMenu rebooting seemingly on its own. At first I thought it was a result of a firmware update (as reported here) and fixed by another update (here), but I was obviously wrong.

My current suspicion is that the slider switch itself is dodgy. When I use it, the display starts switching on and off on its own erratically for a while, but eventually it stops. Since BackupMenu uses the slider switch to bail out of the current operation and reboot and I enter BackupMenu in the critical period, you know what will happen.

I just stopped using the switch and eliminated the problem. To switch the display off, I just use the double-press of the power button. I might look at the slider switch at some point when I open the phone anyway to fix the USB port, but that requires tidying up my desk to make room for the soldering equipment and that may take a while.

OP: might this be your problem?