If it's what I though, it's the famous stamina bug from Nutaku. It seems it's not actual stamina lost, the game just shows you more stamina than you have and cam back to it's actual value after a gather. It's a well known bug """fixed""" many times but it comes back often after an update. It's just really annoyong when you plan to use your stamina for some stages and secret garden and then realize you don't have enough when the stamina is back to it's actual value.
I've never seen something like that on DMM (buton DMM this kind of thing will be fixed quickly with a lot of compensation behind)