I had that Amazon app issue on my HU8550. I reset Smart Hub and the problem hasn't returned. It was after an update by the way.
UN65F9000AFXZA + SEK2500U/ZA firmware version 1162.2
Denon AVR-X5200W, Apple TV, Sony BDP-S6200, PS4, Xbox One
(2) Klipsch RF-82IIs, (2)RS-62IIs (4)RS-52IIs, (2)RS-42IIs, (1)RC-62ii, (2)RB-61IIs
(1) SVS PB12-Plus, (1)Emotiva XPA-100, (1)XPA-200, (1)UPA-200,
UN55HU8550, AVR-S900W, Ceton Echo, Apple TV, Panny BDT460, PC,
(1)Klipsch G-42, (2)G-16s, (2) Bose 161, (1)BIC Acoustech PL-200