Crashes happens a lot, when some players in lobby have strict nat. Solution, set DMZ in router or open ports:
TCP: 1745,1795,3074,27015-27030,27036-27037.
UDP: 1745,1795,3064,3074,4380,27000-27031,27036.
But that not fix for all the crashes, sometimes them still happens. Just load autosave 2-3...