FPS intermittently locking at 2/3 normal FPS

Since the start of Scourge, I have been noticing moments where the game suddenly drops to 30-40 fps for long periods. It can happen at any time -- in town, walking for three seconds in an empty area, more than a minute into heavy combat -- but the GPU usage (NVIDIA GeForce RTX 2080 with Max-Q Design, most recent drivers) shoots from 40% to 97% and the FPS drops to a steady number, usually 38-ish. It will stay there from that point, regardless of any lights, shadows, players, MTX, changes in graphics settings, etc. for an average of two minutes, or until I force a redraw (zoning, changing resolution, etc.). It shoots back up to 60 and stays there until the next time something triggers it, and it repeats the issue (usually within less than a minute). The CPU is under 25% use, the temperature of CPU and GPU are within working parameters, and no settings have changed since Expedition (which did not exhibit this issue). The triggers have included going to the scourged areas (though not always), in multiple instances while using Absolution or Zombies, and occasionally when zoning back into an area from town.

Please let me know if there is any other information you need, and where to post my dxdiag.txt if it would help diagnose. Thank you!