Performance problems in map Savanna

I have very bad performance in the Savanna. My framerate drops down to the single digits and I see bad grey artifacts, as if texture are flicking in and out. It becomes pretty much unplayable.
According to my performance monitoring program, I have about 2 gigs left of unused VRAM while this is happening. Adjusting graphics setting shows no improvement. Of note, near the edge of the map my framerates returns to solid 50+, but if I walk away from the edge I'm lucky to get 10-20 fps

CPU: Ryzen 7 3700 @ 4ghz
GPU: 5700xt
RAM: 16GB