I've been off the game since 2015 and I just started to play again, back when I played regularly to reset a dungeon you just had to walk out of it and enter again, all monster respawn and you could star over, but now the game is not doing that, I know there's a "Dungeon Rest" button, but it doesn't do anything, so How do I reset Dungeons now?

dungeon reset got bugged since yesterday

Great!!! yet another bug...

Well I've been experiencing this since I got back in the game, I need to collect the "Maya's Filler" item and the first 2 weeks it was random that the dungeon didn't reset, but I'm leveling an Thief now and yesterday at Culbert I got this problem

They may have fixed the dungeon reset button with this last patch but we don't know as they don't even post patch notes anymore. One way to reset is to party with someone and disband while inside. It should work.