This sounds like likely to be a hardware fault. If not a faulty screen then a faulty connection or faulty cable. Please try replacing the cable.
It seems there was no secondary screen connected when you opened this bug. Can you tell us what type of connector you are using?
This sounds like likely to be a hardware fault. If not a faulty screen then a faulty connection or faulty cable. Please try replacing the cable.
It seems there was no secondary screen connected when you opened this bug. Can you tell us what type of connector you are using?