I was doing the side quest, "Say No to Feuds", and I went in the Nepeta Mine to kill the Thuggie Miners. After I defeated them, I left the dungeon to team up. When I reentered the dungeon again with someone, there was no mobs to kill and we couldn't go through the door either. I left the dungeon and reentered it alone hoping it would reset, but it didn't. I even tried restarting the client and no luck.
The quest tracker is on and it instructed me to 'Defeat Thuggie Miner' but there is no Thuggie Miner in the dungeon and I can't progress through the door. This is in the Rubal Waste and I 100% guarantee this is a bug/glitch - no questions there. Please fix this!
I had the same problem with this quest and ended up contacting support to resolve it. For me they ended up "finishing" the mines part of the quest so i could move on to the next stage.
I think it has something to do with you leaving partway through the dungeon in order to team up for it. As it happened pretty much the same way for me too.
Go into the Nepeta Mine after accepting the quest "Say No To Feuds".
Defeat the mobs in the first map.
Walk through the door.
Port to Caravan and try going back in again from either Team Up or the Sigil.
It should show there are no mobs to defeat and that you can't pass through the door.
I think something got mixed up with the programming of the game, because 'Dungeon Recall' doesn't show up when I'm in Rubal Wastes, but it shows up when I'm anywhere else.