I had forgotten the prior disussions of this issue which had made it clear that this was believed to be a "software key sticking" rather than the more typical hardware key sticking.
Unfortunately, this is something that's extremely difficult to tease out the root cause of, particularly if it cannot be reliably replicated. And given the number of layers involved between Windows, the screen reader(s), and the programs being accessed with them the "sticking point" could be coming about by a very specific confluence of events that just doesn't happen often at all, and that no one has ever figured out how to intentionally trigger.
Computer bugs really can't be solved if you can't find a way to make them reliably occur. Without that, you can't trace the code path or paths being taken and where the issue finally shows itself. The old programmers wry joke phrase, "That's not a bug, it's a feature," has its roots in situations like this.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
The difference between a top-flight creative man and the hack is his ability to express powerful meanings indirectly.
~ Vance Packard