Thanks Chris … I’m definitely winging it and have little understanding of how things work, but in searching github I saw this update for the SmartThings MotionV4 sensor:
Which shows you updating it for OH3 … so I made an assumption 
that other devices needed to be updated. obviously incorrectly.
And this is unrelated to this post, but in that code it shows the Motionv4 with Illuminance channel which I don’t believe exists. I posted about that here:
Anyway, back to this issue, the device is reporting Temperature regularly so I am assuming it wakes up to do that. If I disable and re-enable it the device comes back online. I turned on the various zigbee debug logs and disabled it, and then reenabled it and waited it to show online then selected Initialize and hit save. Here is the log (filtered just for this device):
Zigbee859E_log.txt (69.4 KB)
Not sure what else to try. The device works fine in my SH setup and I have 20 other zigbee devices working well on OH3.
Thanks for any help or ideas you can provide.