Path Tracer glitches FKControlRig Skeletal Mesh keyframe animation UE5.1

I have a character animated directly in Sequencer intended for cinematic use, using keyframe animations and a FKControlRig. I want to render it using Path Tracer because I’m using subsurface scattering and the environment has lots of trees that look a lot better with Path Tracer. I have had SO MANY problems with this.

First of all, my specs:
x1 Nvidia GeForce RTX 4090
64GB RAM (running at ~50% effort or less while rendering)
CPU is Intel Core i9 13th 13900k

I’m running a large open world UE5.1 file with forest and desert biomes using Landscape Grasstypes and Paint. Nanite is enabled for all grasstype meshes. I then have Sequences set with cameras and I’m rendering one sequence at a time, each about 1 minute. My lighting is just an HDRI dome and a directional light. I’ll note the problems and what I managed to solve so far.

  1. At first Path Tracer was crashing the render every time I tried it in both Render Queue and the Legacy Renderer. I increased r.Nanite.MaxNodes and VisibleClusters until that was solved. I also tweaked r.SkinCache.SceneMemoryLimitInMB.

  2. Now Path Tracer is working with the just with the Legacy Renderer, but my character is glitching, and I’m not getting any wind animation. I can’t see the glitching in the Preview window but it appears on my saved files, whether I save the sequence as JPGs or PNGs, on my PCs hard drive or an external SSD. I’m attaching a screenshot of a corrupted part of the image so you can see.

  3. I tried lowering the resolution of the render, lowering the resolution of the skeletal mesh (which seemed to help a bit and then didn’t, even when I decreased polygons from 1 mil to 50k), putting the animation in a tiny landscape with just 3 trees, rendering the scene in parts, nothing works. I even tried migrating to UE5.3 but encountered the same two problems: character is glitching and trees have no wind effect. Both of these work great when using Lumen.

If I had to pick my battles I would obviously prioritise the character, but solving both would be ideal.

Any advice?