We had confirmed an issue that select dungeons did not have the special 0 Stamina Cost bonus applied to them.
See here for details on the special 0 Stamina Cost event: https://bit.ly/2KRbfc1
This issue has been resolved as of 5/1 (Fri), 4:53 PM (UTC-8).
We sincerely apologize for the inconvenience and appreciate your understanding.
Thank you for playing Puzzle & Dragons.