Bluetooth stopped working

I was getting the ->Bluetooth error

That's not an error. If you get that after you've done https://www.espruino.com/Bangle.js2#resetting-without-loading-any-code then it actually shows that bluetooth is working and a device is connecting to the Bangle (just maybe not the one you intended!).

but I updated on Tuesday, but didn't notice that it wasn't connecting until Wednesday

You mean you updated via https://banglejs.com/apps/ ? Not that you did a firmware update?

How did you test with the DFU connection? Was it with NRF Connect and the watch showing something like on the screen above?