Bangle.js 2 bluetooth stopped working after a month or so

Hi,

I have two Bangle.js 2 watches, one of which is no longer visible over bluetooth (including in the bootloader mode.) As best I can tell, bluetooth is dead on it. For identification below, the working on is 4c9a where the broken one is 4b09.

I did see this similar conversation on the forum:
https://forum.espruino.com/conversations/400107/

Firmware version on both is 2v24. Both have been working well for the month or so that I've had them. I haven't changed the config or charged either of them during the period where broken_4b09 stopped working. Neither device is paired to any phones or computers (that I'm aware of at least. I checked all of mine and I live in house, so no apartment / condo neighbors to worry about.)

I've tried scanning for the device on Windows, Android phone, and from a raspi. Device broken_4b09 doesn't show up in any of them, whereas working_4c9a shows up in all.

Verified in both that Bluetooth settings are Connectable=yes, BLE=checked, Programmable=checked, Privacy=Off, HID=Off, Passkey=None, Whitelist=Off. Both display a Bluetooth symbol in top right that looks identical as far as I can tell.

Looking at forums for troubleshooting ideas, I did a soft reset, a reboot, a power off -> power on cycle, and a factory reset, none of which had any effect. I also booted into the bootloader and into recovery mode where it should have been visible as DFUTarg, but not seeing it on any scans. (The raspi is the most verbose, but not showing up in windows or android during DFU mode.)

Other misc things:

• no corrosion on pins, sticker still over the debug pins
  
• the working_4c9a always showed up on bluetooth scans immediately; the broken_4b09 always took longer (up to 10 s) to be identified, but I never thought anything of it. Could have been a sign of broken/degraded bluetooth from the beginning.
  
• I don't shower with it or wear it during the day. I only use them when sleeping as a sleep quality monitor.
  
• I have no custom apps loaded or any other customization. I'm just using the Health app at the moment, downloading the CSV files and post-processing them with my own scripts.
  
  

Seems very much like this thread, where no resolution was possible:
https://forum.espruino.com/conversations/397947

Also tried flattening the battery until power off, but no dice.