me and my friend had several crashes over the last days. At first they seem to be rather random, but they always happen when one player is in diplomacy and the other player tries to access diplomacy (i.e. double clicking on other factions city). We started several sessions with different factions and it happend regularly.
Build v2.1.2 16516.2700229 (modded):
Better Camera Mod
Disable Startup Splash Screens / Intros
One Button Respec