Reading music from usb

I am using a Naim Uniti star. When I play music from a USB drive, the songs are visible on the main unit. However, when I add new songs to the USB, they do not appear on the main unit. The new songs are visible in the app, and if I rebuild the database in the app, then they also appear on the main unit. I have tested this with three different USB drives, but the same issue occurs. Interestingly, when using an SSD, the songs appear immediately without this problem. It seems that this issue only happens with USB drives.

I would like to know if this is normal behavior, or if it indicates a problem with my unit.

Best regards,