i have been playing the co-op campaine with a friend of mine and about 50% of the time the game will freeze in a loading screen and when it dose load it disconnects the addition player, i have had it happen once where the reconnecting additional player has crashed the host.
I have experienced a similar issue. Me and my brother were attempting to play the Imperium campaign but when our first battle loaded up I loaded up with a glitched view of the battle map and no UI to speak of so I was unable to interact in the fight. Worse still, my game eventually crashed and when it did my brother (the host) was given a mission failed notification. I myself got a "fatal error" message and no crash report to speak of, and before anyone asks I already looked for it as per the instructions on the forum to no avail. Here are some links to the screenshots for what my "battle" looked like.