Sage Doorbell Sensor offline and now won't re-pair

I’ve been trying to get a Sage Doorbell sensor up and running with the Sonoff Zigbee Bridge. It paired successfully a few weeks ago, but I noticed today that it was offline.
I tried removing and re-inserting the battery but it didn’t help.
So I removed the Sage from my ZHA integration and tried to re-add it - it was not detected. I then followed what I believe to be the reset procedure for the Sage

  • Remove battery
  • Press reset button
  • Re-insert battery while still holding reset button
  • When red LED flashes release the reset button.
    I still can’t get ZHA to re-pair with it though.
    Has anyone else had this sort of problem? Any suggestions?