Thanks Kirk, but unfortunately the virus and defrag steps didn't help. There were no detected viruses after a lengthy full scan, and even though the fragmentation level started at 0% I ran the defragger anyway, so it's not surprising that there was no effect. I noticed a few things however that may be beneficial in terms of finding the problem. I ran the maintenance routine on 2 WIN10 pro systems for over 2 hours, each not connected to the internet to make sure there was no possible activity of any kind, one with the steps you suggested and one without, where I selected these two since they could be monitored audibly as I worked (by fan activity on a laptop, and from a noisy drive on the other). On both after between 15 to 20 minutes they became quiet, indicating to me that the maintenance routine had completed even though it reported that it was still active. I manually stopped the maintenance routine and shut the systems down, and on one I received the warning that the "Task Host Window" was running, with the comment "Task Host is stopping backend tasks" with the path \Microsoft\Windows\AppListBackup\Backup, and a forced shutdown is required when this is seen. This is something I see in all of 4 of my WIN10 pro systems, but only intermittently, where a pure guess would maybe be 30% of the time. This warning was never seen prior to June/July period. I couldn't find anything labelled "Task Host" in the task manager when cancelling the shutdown, but the warning still appeared when trying to shutdown again. My guess is that "Task Host" is somehow being launched near the end of the maintenance process and blocks it from exiting, but that doesn't quite fit since I'd think that the shutdown warning would always appear.
I'd think this would be easy to confirm on any system that runs WIN10 pro. Do you not observe the same behavior there? Just manually start the maintenance routine and see if it completes in 10 to 20 minutes. And if not halt it and shutdown. To get the "Task Host" warning may take a few iterations of this process since it's intermittent, but I think it's likely in less than 10 tries.
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