Device randomly turning itself on - any debug tips?

I have a Zwave switch (power relay) that occasionally turns itself on, or that is what I think looking at the IDE logs. It controls a whole house fan, so the behavior is a problem this time of year.

The log doesn’t show any app triggering it; the “eventSource” field says DEVICE which I interpret to mean the device itself. I’m not an expert at reading these values… is there any other info I can glean from the information for the “on” event? Or any suggested fixes? (It happens only every few months, but happened twice this last week – and the problem predated the new app transition. I did create a webcore piston to monitor when the device turns on and alerts me to that, somewhat mitigating but not a fix).

Your not alone, I have a zwave plug that mysteriously turns itself on, it runs a set of led lights, the Mrs keeps giving me ear ache about the lights coming on but for the life of me I cannot figure out why the plug switches on, like you I have checked the IDE for associated automations, I have checked the quick automations but nothing gives any hint of why

Just a mystery I live with tbh

Having a link to associated automations on the devices page would be a great start to troubleshooting but I have given up wishing for that miracle

Have you considered if it could be related to micro power supply interruptions? Device power supplies typically have electrolyte capacitors to absorb these micro-cuts, but some capacity may have been lost.
I have a 3A brand zigbee switch, which is more sensitive to micro-cuts and it turns on some times. In the IDE device events you only see the change to the “On” state, but in the hub events you can see a “zbjoint” event when it reconnects to the hub coinciding with the time.
I put some event captures of the switch and the hub
I don’t know if zwave devices would also see something in the hub events

Some zwave devices have settings to determine the state after a power interruption, like this fibaro switch.

some zigbee switches have it too, but smartthings don’t handle those settings. I have some samotech MS104Z that in the “Tuya” “smart life” app you can set that parameter to “off”, “on”, “restore status” and then install it in Smartthings and keep that setting.

I checked the hub’s event log and it has nothing at the time of the device’s event. But a good suggestion to check there.