My card was covered in pies, didn't clean it throughout the event. Cleaned it just now, no stamina recovery.

So either the bug is only affecting some people, or there is another trigger.

Eitherway, I advise you to not search for it and exploit it, like nip101 said: its not worth getting banned over. Especially in between events when stamina means 0 (and with the shards coming, stamina won't mean anything for a while)