This game is decrease entry count when you enter the dungeon.
Just change to decrease when someone in party member take damage on monster and object in dungeon while enter.
Or decrease when 60 second left that mean dungeon will start and decrease the dungeon entry count.
Then if someone has left just put de-buff dungeon banned.
That mean if that player left or disconnect without clear the old run. He will cannot run the dungeon 10-15 minute.
For queue system need to remake. People can join not finish run the party and popup him ask to join not finish dungeon.