After some own testing it appears that If you have a trigger which refers to a flyable client air unit like ..group in zone Hawg 1-1, zone x, flag on xx, AND nobody occupies that flyable slot when unpausing, the game will crash. If that slot is occupied it will start!
This is what I found out just now, however I have not tested with other people in multi player environment yet. It could also be several other bugs but I think this is one.