While we aim to provide a consistent Tubi experience across all supported devices, we do sometimes test out new content on a limited-device basis before offering it everywhere.
Movies and shows that are available on web/mobile only will not be visible when you open Tubi on other devices, even if you've added them to your queue previously. However, when you open Tubi on your phone or web browser, the titles will still be there, ready to watch.
Protip: You can help get limited-device content expanded to other devices: watch them! The more that people watch the movies and TV shows on web/mobile, the more likely we are to expand their availability to all platforms!