Personally I'd use 433. Sounds like it's lost it's communication.
Do you have any form of feedback on the remote to prove it has a connection to the processor ? For example I have the time on every page. If there's no connection there's no time.
You could always put the reconnect to zigbee command on the remote somewhere for him to press if it is disconnecting.
But like I said go with 433 and that might prove more reliable ?
How far away is the remote from the zigbee ? Did you do the counter driver check ?
