Audio buffering but never playing

I’m having the most bizarre problem with audio files that’s defying all my attempts to rationalise it! I have the Audio Player plugin, and adding mp3 content via the ‘Add Media’ button doesn’t work properly – the result is [audio mp3="site.net/1.mp3"] which just buffers and never plays. If I modify the result to [audio:http://site.net/1.mp3] the file plays perfectly. However, viewed on a mobile platform, NEITHER file plays.

If I disable the plugin, BOTH files play fine on my mobile phone, but in my browser (Chrome), neither work. What on Earth???!