Unfortunately, it can happen that the Apple TV app shifts the setting for the preferred content provider for shows that are available from multiple content providers. Reasons include availability changes for which content providers, differences in episode numbering, differences in availability date/time between the content providers (mainly for new episodes; one cp might be faster than another).
- When you see this happening, go to the Details page for the show or episode, scroll down to How to Watch, and set the wanted content provider there.
- If the issue persists, then remove the show entry from Up Next, and start watching your episode from the intended content provider (e.g. from the Library for tv/iTunes Store content). The Apple TV app should then automatically add it to Up Next again, with the correct content provider linking.