I have unlocked all 5 chests at Temple of Seasons, yet it still shows my secret completion as 4/5 on the map. Checked multiple times that I indeed had 5 "opened chests" in the area, so unless there's another secret other than the chests, it's probably a bug.
This is the only thing blocking me from 100% story mode completion at the moment.
This is the only thing blocking me from 100% story mode completion at the moment.