Oh, I may know what it is. Similar to an issue the Sims 3 had, actually almost identical.
Only twice this month, July 2019, has it happened. And only twice have I ever used the showhiddenobjects cheat plus the new showliveeditobjects cheat.
That cheat, showhiddenobjects, I believe it was called, did issues for Sims 3 as well when trying to close the game.
My game will save but won't close down. I gotta do Alt + Tab to close the window. I've Win10 as well and it was recently updated to help issues.
If I enter in the showhiddenobjects cheat again, will it turn it off? I also had moveobjects on but that never causes any issues when saving & closing the game.
I'll see if I can reproduce this if I am correct and I'll come back here to let you know.