Secrets of the Universe (2014)[1] has eight episodes, but they're numbered 1, 2, 3, 5, 5, 6, 6, 7 on Amazon Prime. When I try to download them with AnyStream Plus, it only lists the first episodes numbered 5 and 6[2], so I can only download six of the eight episodes.
1: https://www.amazon.com/gp/video/detail/B00WTA81F0
2: https://imgur.com/a/t7Klm1b
1: https://www.amazon.com/gp/video/detail/B00WTA81F0
2: https://imgur.com/a/t7Klm1b