Nice catch, that could be it.
My problem went away when I tried doing a clean install of the Windows April Update on my NVMe, instead of the Oct Update. And so far everything is working fine while still having my old SSD system drive mounted (also on the April Update). So perhaps the issue was having both an Oct and Apr build mounted at the same time. However I think I did have the NVMe mounted solo during some of my testing yesterday (Oct build only) and still had the problem.
I'm going to leave this question unanswered for now in case I gain more insight from testing this weekend. Is anyone else here running the Windows Oct Update with no issues?