Greetings, mortals.
We are very aware of performance issues and this matter is our main priority right now, along with expanding game content (new sub-levels).
The main reason for this is that dungeons are never disposed in the current state of the game; all dropped items, living Foes and also the dungeons itself are accumulating while a match still running, this affects specially the server (whose invites other players),There are also some areas that just need some cleaning and receive performance-wise techniques (like the Desert).
As an workaround, you can restart the game before entering a new dungeon. Don't be afraid to do so, Dungeon Crowley design aims a seamless game-play; your character will always be persisted (saved), only the dungeons will be re-generated once you start a new match.
We really appreciate your attention. We're glad that a lot of you guys are having fun with the game. Thanks for playing.
Stay tuned for the upcoming patches.