I was 99% certain it was an engine issue. I've seen so many f'ed up shadows from Assetto Corsa screenshots. Some are much worse than others, of course. An update? I'm sick as sick can be. What a good excuse to go put a couple hundred miles on the odometers of those cars.
I've seen some mods here and there to even turn the shadows off completely. I guess I've learned to live with it, once I've tried messing with shadow bias on some ini file, got so-so results, but never fully fixed the issue.