Disconnection in cooperative game very often

Put the summary of the bug you're having here
In cooperative game when partner connects to me, connection crashes every 2-6 min.
In version 0.5.0 connection in cooperative game was stable.

What I expected to happen was...:
Describe what you thought should happen here

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. Friend connects to me. We play 2 or 3 min. Then the connection crashes. Don't know the reason.
3. ...