Have you tried to repair the sensor (long press on the device tile → wheel → maintenance)?
You must wake up the sensor during the repair process.
You can also try to do the repair process near the Homey.
@Peter_Kawa, interesting how you come from the problem of an empty battery to zone activity. Should he now buy a new sensor every time the battery is empty? The main thing is that the flow doesn’t have to be changed? 
(Just kidding)
Btw, there is a script available to repair all the advanced flows if a device must be deleted and re-added:
[HOW-TO][Pro][Cloud] - Tool to FIX (advanced) flows after removing and re-adding devices
