There are so many variables here it’s gonna be hard to pin down.
My guess would be the crashes were the game not playing as nicely with Proton as it could. Maybe try a different version, e.g. non-GE Proton 8 or Experimental.
The weird choppiness and FPS I would guess is your network. I remember when Steam Link features first came out, it worked great but then would become horrible for a couple hours. Everything was wired in, no bandwidth hogs in the house. Well, turns out that since I was using Powerline Ethernet, it would go haywire with the data streaming whenever my girlfriend did laundry. The washer and dryer threw a fuckton of noise into the line 😆 So I bought a long cable and then it was all good.