itunes imports some artist/album directories but fails on another

i had to rebuild my library when i downgraded to high sierra (needed for legacy apps) so i put all my artist/album directories in auto add, which worked for all but 1 artist. 1 of the album dirs' songs were imported, but into unknown/unknown, the other dirs were ignored-\

so i tried d&d, same/same-\ so i gave up & selected the tracks in unk/unk, & manually set artist/album info, which worked for the 1st album, but failed on subsequents...

w-t-f apple-{