Plutonium

Tesla15 Tu antivirus esta interfiriendo, porfavor, coloca como excepción la carpeta "%localappdata%/Plutonium" (sin las comillas) y debería de funcionar. Sino, no olvides contármelo para encontrar una solución.

Use "Windowed (Fullscreen)"

The same happened to me.
The only thing I did to prevent that from happening was defragment my hard drive.
That doesn't fix the problem entirely, but at least it won't stay frozen for long.
Another solution I can offer is to play 1 game (max 5 rounds) solo before playing co-op. For whatever reason it worked for me.
And the ultimate solution is to switch to an SSD.