Verify that the intended account is selected as active. It is possible to register multiple Apple Accounts within the Apple TV app, and switch between them. Movies are only available when the account, for which the movies are purchased, is selected as active. Additionally, when a child account or profile is selected, some content may be hidden, depending on age of that user and the content age restrictions. It is also possible to set restrictions to a lower age limit than advised for your country or region.
Apple TV app user guide for smart TVs and third party streaming devices - Apple Support
- Try signing out for your account in the app, then sign in again.
- Try finding the title in the Store or through Search, instead of looking in your Library. It should be available there too, also with a Play button (instead of a Buy button).
While it is theoretically possible for a specific movie title to disappear from the Store, and following that also from your Library, for reasons of rights holder (studio) complications, it would be very unlikely to happen to 20 movies at once. I suspect that something else is happening.
If your issues continue after researching the above, then consider contacting the Apple Support staff. They can look into your account and verify what is going on. Contact Apple for support and service (phone numbers) or start your support request online (chat/email/callback).
