Now that the exams is done I can come back and try to fix this.



Notice the music choises in the upper part of the left menu and the music note on the lower left. In most folders you can change this, but not in the folders I mentioned in the first post, as you evidently can see here.



Here's an example of how most folder's options look like and here's also the displaying mode that freaked out and either directly or indirectly caused the still remaining issue.
Displayed as this, every folder and file (tested a bit) wouldn't diplay the name, no matter what, in that particular folder.