Been around since iOS 8 beta 1. Still not fixed in the 8.3 betas, but things HAVE improved with 8.3, at least... anyway, the bug description: The iPhone's ability to handle data requests worsens with time. Responses get slower and slower until failing outright, even with ideal network conditions, on both Wi-Fi and LTE / 4G / 3G. A hard reboot of the iPhone clears it up, but it always comes back. I hope this is fixed in iOS 9, 'cause it's driving me batty. Affected BOTH iPhones I installed iOS 8 on (a 5C and a 6 Plus), too!