Apple Watch Series 2 won’t start or reset - keeps cycling back to “erase all content and settings”

I started having an issue where after a workout, the LED HR monitor would not turn off, even if I X-ed out of the workout app. It got so that I had to reboot the watch every time after a workout (I read heaps of discussions about this, but none resolved it).

Then today, the SOS started going off repeatedly while I was just reading (so not touching the watch or holding my arm in some weird way to press buttons). Then, after a workout, I rebooted the watch as usual, but it failed to reboot altogether. I then tried hard reboot (press both buttons, wait for Apple icon), and was then presented with the “Erase all content and settings” option (see photo).

I selected “Erase all content and settings,” bc I thought I could just set it up as a new watch easily enough. But after selecting it, I got to the normal little ticker wheel that shows you that it’s erasing/updating (see second photo), and then instead of erasing, it just goes back to the same red bar with “Erase all content and settings.” I have selected that several times now, and each time it tries to erase, but then just goes back to the same option. As it sits here beside me, without my touching it, it is periodically flashing back to the Apple icon, and then returning to the “Erase all content and settings” option.

Any suggestions?