Coverimages from Network Music Folders

Hi, here’s something that I don’t fully understand. I have Volumio installed on a Raspberry 4 with a 32GB card. The original 7-inch touch display is connected to the Raspberry. Now I have the following phenomenon. If I access the music collection via the network via the browser on the PC or via the Android app (samba), I see the cover images displayed there. But unfortunately not on the display on the device. This is the case for a short time after re-reading a folder, but then no longer. Does anyone have an idea what that could be?