I am having a similar issue
Whenever I enter a MP server the game crashes with a c++ runtime error on the second screen. Not the loading one but the one where you select your plane. It's loading but then it just crashes. SP works fine so far.
It is a fresh install (since yesterday) and no mods either.
I attached my logs, if someone could take a look I'd greatly appreciate it.
Edit: For some reason when joining the servers with the Beta client it works just fine... Guess I was just using the wrong client then log.rar