iOS 8.4 was made available at the end of June 2015 and brought several new changes to iOS – with the main one being Apple Music, plus some changes for iBooks and some bug fixes.
iOS 8.4 info
http://www.gottabemobile.com/2015/07/02/ios-8-4-for-iphone-ipad-10-things-to-expect-now/
http://www.trustedreviews.com/opinions/ios-8-4-beta-features
Some users have complained of all sorts of issues with Apple Music and their existing iTunes library – http://www.forbes.com/sites/ewanspence/2015/07/10/apple-news-digest-apple-music-itunes-iphone-6s/
And also, some users are reporting issues with wi-fi – that old chestnut!
http://www.forbes.com/sites/gordonkelly/2015/07/24/apple-ios-8-4-old-foe/
There’s expected to be an iOS 8.4.1 release coming up – http://www.gottabemobile.com/2015/07/28/ios-8-4-1-update-5-things-we-learned-in-july/