I have three of these that have just started in the last few days turning themselves on every day at around 3pm but not the exact same time every day.
They are connected to my Hue bridge, which is in turn linked to my Hubitat hub
I am pretty certain this is not a Hubitat problem as the logs and events show nothing for these devices. I have checked any rules they are connected with and there are no timed automations.
Opening the Hue app, the lights are not shown as on when this happens. They are unresponsive to being turned off, but responsive to being turned on, which makes them controllable again by both Hue directly and Hubitat interface.
I think I have ruled out a power interruption, as when I turn off and on the wall switch to test, they don't come on at the same colour and brightness as happens when this strange thing happens. Ie that's not what I set as their power on default.
I have been into my Hue account online, checked no one else has access to it, disconnected any apps that I am not certain of, including labs and essentials.
They are not visible to Google or Alexa other than via Hubitat. So if either of these helpful assistants was sending commands I would expect an event to show.