I have same issue with 2001 a Space Odissey. Bought the movie in a Kubrick collection. All other films are available to be viewed and download, just this one is aasking me to pay again.
All happened after 12.3 upgrade.
Contacted Apple support, response is "dear customer version has changed, please buy again!!!". No comment!
Just unacceptable!
Hope this will be fixed in next update of AppleTV OS.
By the way I do have also a collection of all Harry Potter movies, which where upgraded to 4K already sometime ago. The first day after upgrade of Apple TV just the First part was in 4K, all others in HD. A couple of days later also the other episodes where put back available in 4K.