This problem is pretty interesting and unique I guess.
So If my friend joins to a lobby and plays about 2 minutes, she receives the “lost connection” error and the game freezez. When she creates a lobby and I join her (and some other players) we also receives this “lost connection” error after few minutes of gameplay. Everybody, the only exception is she.
She doesn’t have the new DLC. Before the new DLC she didn’t have this problem.
She also sent me her log file. If it’s necessary I can send it for examination.