It does not feel good at all if you got dc during challenge map. These are the things that will stop me from playing. It inly happened to me once so far but boy I tell you, It made me quit for the day! If this always happens, which is very likely, it would mean quiting the game.
Allow partied players to go through the portal. Remove timer and make the portal party bound. Only the first party in can enter.
Please address this issue ASAP. No one likes this.