Figured it out -> reproducible:
- Take battery out of the sensor
- Short the positive and negative terminals of the sensor itself
- Set hub in zigbee pairing mode
- Insert battery (The sensor is now found, but not initializing)
- Remove battery for a second
- Re-insert battery (Initializing completes as normal)
Both the old sensor (SNZB-02) as the ne sensor (SNZB-02P) paired this way, and seem to continue to work al normal.
Still strange, as this was never needed before.