Have you experimented with any new Zigbee switches at this time?
I have experienced the same at least twice, when experimenting with an Aqara double rocker switch and Osram Lightify remote.
This should have been a Zigbee Group #0 broadcast sent by something. There is no way to log which device made the broadcast.
[physical] in the logs means, that the switch on operation was not initiated from the driver or from any app.
