I’m having an issue on the Apple TV 4K with cover art missing from the Watching or Recently Added section at the top of Infuse. All cover art has been added via iTunes and most of these files are .mp4. Some shows do not show a screen cap or cover art at all but instead show a gray default banner. What causes this? The cover art shows correctly in every other area of the app. Also, sometimes the same file will show the covert art on one Apple TV, but not another one in the same house.
I had the same issue. I found a solution on another post.
Go to Settings and toggle Metadata Fetching off and then back on.
That worked for me. I hope this works for you too.