Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
I have a recent Samsung 4K TV connected to a Roku Ultra. When I watch Prime Video content (current Bosch in 4K) sometimes the display is very strange (sort of like a pointillist version if you're familiar with that art style --- outlines of shapes but color pixel dust). Sometimes I have been able to "fix" the problem by (say) watching some 4K Netflix content after which he Prime Video display is fine. Sometimes it's crankier. I removed and reinstalled the app, and reset the system, neither of which seemed to have any impact.
What model TV? The early Samsung 4K sets (like mine) only have quasi-HDR support, and perhaps that might be causing a problem. However, I have watched some UHD HDR material from Amazon recently and didn't have that particular issue. . When you removed the Amazon channel, did you restart the Roku (unplug for 30 seconds then power back up)? If not, you didn't completely remove it and if there was an install problem it's still there.
Dan Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.