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 1151.4
Denon AVR-2313ci, Apple TV, Sony BDP-S6200, PS4, Xbox One
(2) Klipsch F-30s, (2) Klipsch F-20s, (2) Klipsch S-20s, (1) Klipsch RC-62II
(2) Klipsch S-10s, (2) Klipsch B-20s, (1) Klipsch Sub-12HG
UN55HU8550, AVR-S900W, Ceton Echo, Apple TV, Panny BDT460, PC
(1)Klipsch G-42, (2) Klipsch G-16s, (2) Bose 161, (1)BIC Acoustech PL-200