Puzzle: How to track down what is causing frequent bulb on/off?

[worldly turtle]

For some years I have many bulbs controlled by HA using ZHA.
Recently just one bulb (a basic RGB model from Lidl) has a history of turning on about every hour for 1-15 minutes and then turning off. See history view that shows this, even through the night hours when we're all asleep.
The bulb is part of 2 automations. But I have checked their logs and they are only firing when they should.
The Activity log on the bulb itself confirms its turning on and off, but doesn't show what triggers it.
Other similar bulbs aren't showing this.
Please, what else can I use to debug what's causing this?

[royal flume]

Are you able to set its default state on power up?
It could be crashing/rebooting then turning on because that is its default state?

[frail kelp]

If HA does not print a reason for a state change, the change is not cause by HA itself. That leaves

• Bulb itself (spontaneous or power on behavior)
• External control
• Zigbee groups

[worldly turtle]

Good idea. I've looked through the Zigbee details, but can't see any way to set default state. I have though tried reconfiguring the item, so we'll see if that helps.

[worldly turtle]

Thank you for that helpful list. I confirm it's not external control, and its not in a group. So after I try the Zigbee reconfiguration, I will try unplugging the bulb for some hours and see if that helps.