I have the same problem. Me I my friend are playing on LAN. When we startego to play on BETA everything was just fine but after couple flights that issue have started. Now when I'm host he can play on my server for about 5 to 10 mins and the same thing is when I'm connecting to his server. Also I've opened ports on my router. Another weird thing is that my ping on other games like arma or wot is from 15 to ~60 so it is on DCS servers like going ugly but when I connect friends server its always ~125... I dont get it... Its just so fuc...up...
Guys your methods like fog of war, mp LAN connections etc dont work for me...