OK, I can guess.
For some reason Calibre is now opening that form
off screen
Try this while it is supposed to be there
Alt+spacebar then M then use the left arrow key a bunch of times
If this is working, you should see the form enough to drag it back to its favored location.
The unanswered question: Why is this happening (besides it came with the 4.x update, migrating calibre itself from Qt WebKit to Qt WebEngine, because the former is no longer maintained). Where is the RAID guy