Unity crashing efter losing connection to other Unity

I have two Unity Editors running two different projects. One project is a clone of the other (same game on both editors).

It's a network game. One Unity Editor is connecting to the other (the Play button is pressed in both instances of Unity).

When I stop playing in one Unity Editor the other Unity Editor (which is still playing) crashes and I have to start it again. It doesn't happen every time, only sometimes. Pretty often, though...

Why is this? It should just lose connection and keep running but instead it crashes. Any ideas how I can find out what is wrong? The game only crashes when running inside the Unity Editor, it never crash if I export to a stand-alone exe file.