Intermittent All On

I have a customer with a very basic system consisting of dimmers, relays, key inputs and a few sensors. No screen, wiser, PAC, no scene control.
Every so often, fortnightly maybe, everything turns on. Usually at night. Everything can be turned off but you need to walk around the entire home to do this.
I thought it could be a comms wiring issue but this has been fully checked. Haven't been able to check the log as it never happens when I'm on site.

Any thoughts?

 

This is most likely caused but leakage across the remote on connections somewhere in the cabling. Any sort of contamination from water or rodents etc can cause this. Neither the remote on or remote off pairs are ever needed in a domestic install but they are often connected through anyway. You could check each termination individually, or if all output units are in a single enclosure, just try disconnecting the remote on/off pairs going into the enclusure.