[MercenaryMuffin]

I believe I may have found, at the very least, part of the problem. I can run the ground detail settings at Excellent, but not Perfect. Which is weird, because I used to run it at Perfect all the time, and it has only given me trouble recently. I went to change the ground detail to Perfect after running all the CCC checks you said, and sure enough, the ground went black. I changed it back to Excellent and it seems to be okay.

Shame I can't see ground detail at its highest, but if it means less game interruptions, so be it.

Thanks for your help, I'll post here if anything pops up again.