When the problem first started occuring, OBS was not installed at all.

In-game frame rate limiter was being used. I've swapped to a Framerate cap in MSI Afterburner, and even on maximum settings, GPU utilization rarely hits 90%; usually between 70-80.
After an hour of play, there were no slowdowns, no missed animations, even while recording.

Tangentially related, I noticed some slowdown in Windows 10 as well, so I removed any and all overclocking. So running at stock 3600~mhz for the processor (ryzen 5 2600) and 2400 stock MHz for the memory (which should theoretically be able to hit 3k with no issue).

Going to run a Memtest overnight to see if I got a lemon mem stick.