Sonoff zigbee PIR disconnects

I have 8 Sonoff PIR zigbee sensors. In the last few days, 3 of them became ‘unavailable’. One is inside and two are outside where temperatures go down to just above freezing.
I can see the inside one tripping but it doesn’t report to HA. I tried a quick push on the reset - no change. I tried pulling the battery and re-installing - no change. I finally had to pair the sensor to the Sonoff bridge again in order to get it talking.
Is this a known problem for Sonoff (either the PIR or the bridge)?
Is there anything I can do short of going to a different manufacturers PIR?

Additional info: Two of the devices had just about 50% battery life remaining. The third (indoor) device was down to 23% and even with it being reconnected to the bridge it did not work properly until the battery was replaced.
At what % do other people replace batteries ?

A week or two ago I turned on an old AP I wasn’t using to troubleshoot something… wiped out all of my upstairs zigbee lights and remotes. As soon as I changed the channel of the AP they all came back. Any changes to WiFi recently?

Hmmm … I moved an access point (Ubiquity) from one physical location to another.
I will have to keep an eye on that in the future and see if there is any correlation.
Thanks!

I would try either temporarily disabling it or check the channel it’s using and see if it helps at all.

All the devices are back up - I re-paired (chuckle) them.
How do I know what channel zigbee uses and wouldn’t all zigbee devices in the house use the same channel?