I am running group of 5 man bot party and sometimes it happens that at random one of my party non tank/leader leaves dungeon finder. What is happening is after the last boss in dungeon is killed party leader starts new queue for dungeons and then my other party members are joining the queue. In the next dungeon my party members join the dungeon except sometimes it happens that one or two members are not in the new dungeon they are instead idling in the garrison and the dungeon finder icon is not showing on the minimap for those characters. I am not compleatly sure what is happening with those characters that are not in the dungeon because these error is happening at random and always on random character so its impossieable to observe the error behaviour. In the dungeon my leader is idling/waiting for other party members to come close. If i move my leader close to dungeon boss and then characters kills the boss my idling party members will after that join the dungeon. Here is log for my idling character:
I am not sure when it started happening, i know that 20 days ago i was doing draenor dungeons and i didnt have that issue. After that i moved to legion dungeons and dont know if it already started happening at the very begining or maybe a week later i got the error. So proly bugged legion dungeons. Before i wasnt running that long legion dungeons but now am running it more and its certanly noticeable happens like every 2-5 hours.