Howdy again,
I have attempted to recreate the issue with the additional information that you have provided but the error still does not occur on my system. Here is what I have been doing for reference:
I have brought up the editor, tried both full screen and windowed, unplugged both monitors with the editor on each (pending on the editor placement), even disconnected the main view port from the editor but no luck.
Would it be possible to capture a screenshot or perhaps a video so I could further investigate the issue.
Thank you for your patience!