A bug found in the latest iTunes update causes playback issues related to songs streamed via Apple Music that are shorter than 60 seconds (via MacRumors). According to the report, this issue has been replicated on OS X 10.11.5 with the latest iTunes 12.4.1 update.
Specifically, if the song is played in its entirety without being skipped, and is shorter than 60 seconds, the song that is played after will be buffering indefinitely.
It looks like the way AM handles streaming is when the current song is a minute from the end, iTunes signals the next track in the queue to start downloading so that it’s ready to play when the current song is over. However, when the song is less than a minute long the next song’s download is never initiated, apparently because some “one minute remaining” event is never triggered! This means the app just sits waiting for a download to finish that has in fact never started.
It appears to only affect songs that are streamed via Apple Music. Songs that are synced locally are unaffected by this bug. For now, it only seems to be an issue with OS X 10.11.5 and iTunes 12.4.1 as the issue was unable to be reproduced on a Mac running macOS Sierra, or an iPhone running iOS 9.3.2.
