Hmmm... for some reason, I had not been receiving email alerts for replies to this post (not in spam either). But I did receive @Jody Thornton's reply this morning, so I'm back
@Jody Thornton Before reverting to a full-image backup, I tried the following steps:
manually uninstall each month of patches (June, then May, then April), but yielded the same (poor) 3D rendering results. I'm sorry... probably should have mentioned that.
uninstalled (some of) the .net patches too (but can't recall which ones).
disabling, and even Uninstalling MSSE.
finally restored an April Backup (which included all of the March Patches) and it fixed the problem.
@Vistapocalypse Ha... "FrankenVista"... no doubt a rare breed that dabble in such realms Surely this is an exercise in futility, but even Dr. Frankenstein loved his monster in the end.
I read the thread you pointed to, which refers to the updates causing problems KB4089229 & KB4090450. Those are in my restored backup image, so not likely the cause here, but thanks for the suggestion.
I'm very conservative in terms of installing new software, so there's not a lot of other variables. Although I did install Samsung SmartSwitch. I'll make a fresh backup, then install SmartSwitch, and report back (probably within a few weeks). Who knows, some dramatic, dark, rainy night, with thunder & lightening in the background, I'll install the patches in "blocks" (April... test... May... test... June... test) and see if I can isolate the issue so that FrankenVista can continue to live!