Big update. I’ve found the shaders responsible for the performance drops.
They’re standardstaticdetail.ssh and standardstaticdetail_nofade.ssh. Without those, the performance in Kurnhold is stable, high, and smooth. I’ve tried replacing those with the oldest ones I have backed up (1.2.1.2). Unfortunately, those also cause performance issues.
But now, I know for certain that those two - and not individually for some reason, only when they’re both gone does the performance drop get alleviated - are causing at least the issues in Kurnhold.
My methodology? I extracted Shaders.arc with the provided ArchiveTool.exe, gutted shaders individually or in groups and re-compressed until I narrowed it down to the ones that cause the issues.
I’d like to tag devs to look into this as it is now clearly a concrete, specific finding. I’m willing to record videos with frametime monitors to substantiate my claims, even though I suck at screen recording. But it’s there: frametime spikes, render stutters; this is NOT about microstutters/freezes, this is simply about the framerate in Kurnhold (and obviously other places in the world, but this is the easiest to reproduce).