I made a clean install from the latest release of HifiberryOS on the SD card.
Copied music files (previously used on the SDcard and worked fine) to a USB thumbdrive
When I update the library, not all artists are shown.
Updating the library from the commandline gave following result.
Checking things shows all the files in the folders starting from Dionne Warwick are been erased.
As this is a one to one copy and things worked before, I have no clue what's wrong.