I have a Roku Streaming Stick+ connected to a Pioneer AV Receiver connected to a Samsung TV. All apps display correctly on my TV except the Apple TV app. When I open the Apple TV app, it takes a long time to open and when I open a show to watch it, the show is displayed in such a way that the entire screen is not displayed. It is enlarged, zoomed in so that all content cannot be seen. It only does this on the Apple TV app. All other apps display correctly. When it first began happening, within one week of my purchase and installation, I was able to restart the Roku Streaming Stick+ and it would correct the problem but, since then that doesn't work. It's very annoying not to be able to see the content in its full format.
Try this -- don't know if it will help. You can always change it back.
Settings > Display Type
Set to your tv's actual resolution, not "auto".