Yes, that problem that spontaneously cropped up on only my Roku 4K Streaming Stick+ with latest OS. I am on Spectrum cable and Internet. The AMC app was previously running flawlessly, and was authorized, and had the correct login information, etc. but suddenly would just not start up. It would trash out and loop back to the Roku Home screen.
After trying less drastic fixes, like restart, clear cache, and remove/reinstall the channel, I finally resorted to a complete reset to factory defaults. (You will need Internet access and email to do this!!) That purges any patches or incomplete updates in the operating system and proceeds directly to the latest version. Once you log in and it "creates" your account on that Roku device, It will give you the option to either put back all the channels you had, or start fresh. You will need to Activate all independent channels that are tied to your cable subscription and that require a separate login. This is not the first time I've had to reset one of my Roku devices to factory default to clear up some login problem involving Spectrum cable service. However, a reset to factory default has fixed the problem every time.
eta: I have 4 different models of Roku devices made 2016 to current. The Roku Streaming Stick+ 4K is the ONLY one that developed a problem with the AMC channel. eta: The only Roku, this time. I've previously had the same issue with some of the others. I suspect corrupted or incomplete updates are to blame. But I don't really know.
