I have this exactly, only it's in multiplayer as well.
I took some printscreens how it looks like.
https://gyazo.com/93d6ac15c04e9b58573b85a5adda7ec2
https://gyazo.com/6ede414a529d340c165d30b104394a8d
https://gyazo.com/5e3d0e19a981c4ddde704219315496d5
I'll have normal gameplay for around 5 minutes when joining the server.
Then out of nowhere my fps starts dropping from 50-60 to 3-4 and all graphics start going to shit.
The thing I've noticed when that happens is that my disk usage also drops to 0-4% while it's usually somewhere around 40-100%
