This is a new one for me, and it couldn't happen when I'm playing with Fantasy Ferris Wheels, it waits till I'm working on a set of Permit Drawings.
It happens more frequently with large files, but also occasionally occurs with any file. And the frequency is increasing.
So, a file will begin to open, sometimes it does, sometimes it appears it doesn't. If it opens, I can work in that space (model or paper), until I switch to another, then it freezes, but not quite.
When it doesn't open I simply get a grey workspace.
Now look at the first image, vanished 1, you can see the file name at the top, and the rulers around the workspace.
In vanished 2 you can see I clicked on the BLANK screen and opened the selection box of a viewport.
Having switched from modelspace to paperspace, and have nothing happen except the screen going blank, I thought I had lost the drawings, but when I clicked on print preview, there it was. see vanished 3.
If the file does load to model space and I switch to paperspace, nothing seems to happen, except the rulers change, and I can click on paperspace viewports, while the workspace show modelspace. And if I click on print preview, there is the missing paperspace. vanished 4.
At this point the program freezes, though I can close it and it politely asks me if I want to save any changes.
To paraphrase Abe Lincoln, it happens to some of the files all of the time, and all of the files some of the time, but it doesn't happen to all of the files all of the time.
My instinct tells me I need to re-install, but before I do I thought I would see if anyone had any experience with anything like this.