I guess this is a bug of some sort. It happens to me quite often in the last month or so. I have manager open doing some work, then switching to a different application for some time like half an hour or so, then when try to go back to Manager I just get a gray screen, and no companies or other data show up.
Then I have to close it and start it again. So the title bar buttons are visible and clickable but not any of the main screen of Manager.
This is on windows 10 currently running 21.2.40.