After a dungeon party is formed, if someone leaves the party in the dungeon and an attempt to replace the player is made - it is never fulfilled.
In PUGS which is mostly who I play with, rarely are the original 4 members of the party able or willing to finish the dungeon. In the past (maybe a month a go), if a person dropped or was booted from a dungeon party, it was relatively easy to post in the group system and find a replacement within 2-5 minutes. For over a month now, that system has completely failed to work at all. In every single party I have been in where someone drops, the party is FORCED to disband and not complete the dungeon because the Dungeon FInder NEVER finds a replacement. This is a pretty big bug, as Dungeons are a pretty major part of the game.
This has been a consistent bug for me and everyone else I know that plays the game for over a month.