I think what you describe is a flash of colour across the screen that pops up randomly.
This is a known fault and can easily be stopped. The TV keeps listening for sound waiting to hear "Hello Sky" to turn on, other sounds confuse it and it flashes.
On the bottom right corner to the side is a white back lit button, this is the mic - turn it off!
You now won't be able to talk to the TV for voice activations but it will stop random screen flashes. You can still use the remote for voice activation.
If you have had three TVS with this error it beggars belief what the Sky help desk are being told to look out for from callers 🤔
