I wanted to add that I had intermittent Airplay connection on my iphone6. The network connection was good. When I was streaming from Amazon prime, I would get one song playing and the next one would not..each and every time. I would have to manually hit the play button.
What fixed it for me was adjusting the cache size to unlimited on the amazon prime settings. Not sure if this would work for other apps with streaming issues but it did resolve mine.