Not too long ago I setup my Owncloud and was playing with the music player feature, well cool. While uploading an album I noticed that all the songs were group under a folder call unknown. Did a little searching and found a fix on GitHub
Check it.
5.04: had to change "public $option_max_2gb_check = null;" in "3rdparty/getid3/getid3.php" to "public $option_max_2gb_check = false;" else music shows one artist (unknown) with only unknown albums/tracks.
credit to Bobol https://github.com/owncloud/core/issues/3084