blank alias in the dock

Hi,

A I created a folder to organise my applications with aliases. I put this folder in my dock bar next to the original application folder. Everything work perfectly except the icons are blank.

If I open the folder in the finder I can see the icons but in the folder in the dock not. I've done that to work faster et easier than before and without visual it's not effective at all.

By the way I also have some files alias in this folder and they have all blank icon except one that I just create few minutes ago (an excel file).

Can you help me to understand and to fix?

(I'm on Macbook M1, Big Sur 11.3.1)