What happens is that when you arrive in the dungeon after the group has formed and travel there via autotravel, there is this round circle that counts back and your whole group gets booted out of the dungeon, the same way you're forced out of the dungeon and the end when you have defeated the boss and left your group.

This happens +/- 80% of the time, sometimes you stay into the dungeon, most of the times you get booted out and have to manually re-travel to the dungeon, and the rest of the players have to travel towards you when you have arrived in the dungeon.