Suddenly the cistern is only filling after a delay from 2 to 10 seconds whereas it was immediate some days ago. I didn't touch anything and I'm sure noone entered my flat.
Not sure if it is a problem though as there isn't any leaking.
I don't know if it is linked but it seems this
doesn't serve any purpose since the cistern is filling whatever if it is open or closed.
Here is the best picture I could take: