I am using zoneminder to monitor our church facilities after four breakins

It has been working REALLY well, but...
I have noticed lately that one of three grandtech cameras that were all working fine has suddenly started turning itself off

I have it changing from monitor to modect at night and then back to monitor during the day, all via a cron job, which seems to be working perfectly

When I go in to check the system the camera in question has turned off the 'enable' tick in the config. I turn it back on and it accepts the change (the console has the camera all back to orange - if it is in moitor mode - or green if it is in modect mode). Come back some time later and it is red again (mumble, mumble).
I know that no-one else is playing with it (for fear of broken fingers

I have checked the forums but cannot find anything like this behaviour.
Any idea where I can start troubleshooting?
After another broken window last night I am keen to fix this ASAP.
Thanks
Jerji