the challenge dr has been freezing on us a lot of times recently and costing some teams FF & to start late in games. I think there is a solution. Tell the team that is sending to only send when there are 5 or less people in the challenge DR. Then try joining the game with all 6 of your players. This has worked for us recently.
Put both of your hands just above your head and jump on one leg 3 times. Everyone in the dr must do it at the same time. That should fix it.