I think I found a bug in ArcGIS Pro when using 2 screen on the same computer. Some windows are disappearing when I try to move them. This bug only happen when I use ArcGIS Pro inside the secondary screen.
Step to reproduce:
Here is an exemple:
I am using ArcGIS Pro 2.2.0. I can't test with 2.4.2 (I don't have admin right on this computer so can't upgrade). Maybe the bug is already corrected in the last version?
Nicolas - I'm using AGP 2.4.2 and followed your steps precisely. I don't see the same behavior that you do. Perhaps it has been fixed/addressed in a later release.