Computer is fixed. It seems that there was some mouse software that was installed with the Microsoft Mouse back when the computer had Windows 8 on it. It was meant to activate the two side buttons and a press of the scroll wheel, things I've never actually used. The software got corrupted some how and was intermittently turning on some kind of task view function.
The clue was I couldn't change the mouse cursor back to black. After extensive testing and finding nothing wrong with the computer, the tech took that cue and removed the mouse software. Now it's back to the mouse software that Lenovo put in (which is the one I always used anyway).
The problem seems fixed, as it's been working all day.
And I'm $80 less affluent

but my computer is working

and I can use PG Music's Power Tracks Pro again without the screen weirdness popping up in the middle of a session!!!
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