Secret Room Above the History of Magic Class

[Zeroicetea0]

I have noticed that early in the game while your MC is doing the Hufflepuff student's treasure hunt quest that you use Accio on a portrait for a door in the painting reveal itself; that there is this wooden block and the bookcase next to the fossil display, and there is a room showing in the minimap behind it.

However, the block and the bookcase disappears later in the game; I confirmed that with all 3 of my characters. In my last gameplay, they disappeared after my MC learns "Confringo".

Has anyone figured out the reasons why the blocks and the bookcase or how to access to the room behind the display?

Many thanks in advance.

https://imgur.com/a/E05DUi2