From the FAQ section of the walkthrough:
"You
need to turn every switch once (to the left), but the switch in the
flame riddle room has to be set back (after obtaining the chest). In
the top right are 3 switches close to each other. The lowest of those
three also needs to be turned back after the other two are active."
As shown in the image of the other thread: https://itch.io/t/849335/leilles-dungeon