constant infinite loops requiring program to be closed using task manager

Symptom is that the program hangs up after I've clicked the mouse to select some element; after opening a score I'm getting anywhere from 3 to 10 working mouse clicks and then I get the blue wheel of death. This happens when clicking on an existing note in preparation for moving it, or clicking on a bar in preparation for adding/removing bars; it seems to be associated with the use of the mouse rather than tied to any particular kind of element being selected, but I can't be sure of that. After the hangup the program can't be closed from within: must use Task Manager to End Task. Rebooting the computer & creating a new score from scratch doesn't solve it. This is a new problem that I've never experienced before in years of using MuseScore frequently; when arranging parts I use the mouse a lot to move entered notes and adjust number of bars and don't ever recall seeing this issue before. I have not knowingly changed anything on my computer or within MuseScore. Whatever the problem is, it's making the program essentially impossible to use. I'm using the latest version of MuseScore (3.6.2......) under Windows 10 Home. Searched the forums & can't find anyone else having this problem. Thanks for any help. UPDATE: PROBLEM DISAPPEARED AFTER ABOUT THREE HOURS!?!! SO DON'T SPEND TIME ON THIS.