HRM Pro Plus suddenly stopped pairing

I have a HRM Pro Plus that I purchased new in January 2023. It has suddenly stopped pairing, or even being seen for pairing. This is happening whether it's with my Edge 830, Zwift, or Rouvy.

I've replaced the battery, removed it from the 830 and the indoor apps. It also doesn't show up as a bluetooth device on my phone.

Any thoughts would be appreciated.