This is the Happy Dungeons Management Team.
Right now, there are the following issues in Happy Dungeons:

We have acknowledged the problem and we are currently working to fix it. We will post more details in future announcements.
We apologize for any inconvenience this may have caused.

Update: on August 13, the problem has been solved.
The game needs to have the latest data to work properly.
In case you are playing at the moment, please return to the title screen to update the game.