As an experiment, we tried creating a new user and logging in with Unity, and the problem vanished! It drives the external monitor just fine.
If I then switch over to Jane's account, it exhibits the same problem.
But then I can switch back to my account, and it works again!
As an experiment, we tried creating a new user and logging in with Unity, and the problem vanished! It drives the external monitor just fine.
If I then switch over to Jane's account, it exhibits the same problem.
But then I can switch back to my account, and it works again!