The threshold limit the disables the Light of Deldrimor has been set such that you are not able to uncover treasures in the far back corner of the Sauna room.
The Light of Deldrimor indicator points towards a corner of the back room, as seen below.
However, when trying to uncover it, the Light simply fizzles, like it would outside the puzzle rooms, and does not spawn the Hidden Chests.
"Thief? How rude! I'm a Procurement Specialist." -Glenn Gynnafante