Two issues I have noted and will report: 1) Slow response changing tracks in Music - not streaming but downloaded files. There is often a 5 to 10 second delay if you click to play the next track on a playlist or in an album. There is no lag between tracks if you let them play in full, it only happens if you want to go forward to the next track before the one you are currently playing ends. 2) There is a much longer delay (minutes) when selecting Purchased AAC files to play. These are files from the era when iTunes Store music files were protected and you had to be signed in to play them. The problem does not manifest itself when playing recent purchases. Is this because the file and the Music app are trying to verify ownership?