Update:
It hasn’t been perfect. After posting the above, I worked with cubase for many hours and did some live recording which was mostly great. Had a wonderful time. The issue never came back the way it was originally, but I did see CPU spikes again which generated at least one small pop and threatened to a few more times. The issue is suppressed, but it lurks.
So I rebuilt my workstation and stripped every driver and component that was not immediately necessary, and step by step, rebuilt each item and tested for ASIO/cubase issues. The PC Im using is empty aside from cubase 10.5, and now Ive introduced the VIP software that comes with my Akai Advance49 controller, which is a 64bit VST host. So far so good.
Looks like cubase/ASIO and/or microsoft isnt going to make this easy for right now, at least until someone patches something to improve this, so Im using high ASIO guard, high priority on my CPU, and the most stripped-down windows10 build I can manage. I recorded 5 hours of live ambient sets and built some tracks last night, and I might have heard a pop ONCE when I got too high and mashed everything for fun.