Plutonium

Hello, I have a problem, when I want to play with my friends in a private match_private match_ I double-click on my friend who is the host then I get the join game session poster but after 3 seconds the poster disappears and does not join the game , I have not found any solution so far, could someone help me?
The worst is because my other friends can join him and I'm the only one who can't.