Hello,
This may not be related to your issue but I once thought my library had missing movies but in reality a filter was on that was hiding any movies I had already watched.
Library in the Apple TV app - Apple Support
"In the menu bar, navigate to Library, then browse items, or select a category or genre to filter items."
Adjust Apple TV app settings - Apple Support
"Remove information about what you’ve watched (which is synced with the Apple TV app on other devices): Select Clear Play History. This also removes TV shows and movies from Up Next."
If you were using the same Apple ID for all the purchases they should stay in your library.
Redownload TV shows and movies that you purchased - Apple Support
"How to redownload TV shows and movies on Apple TV and other devices
You can't download movies and TV shows on Apple TV, smart TVs, and other streaming devices with the Apple TV app. You can stream movies and TV shows that you purchased. Just open the Apple TV app and go to your library.
Don't see the movie or TV show that your purchased?"
I hope this helps.