This is not true....was able to download 'Halo' with only one episode available the same day it was available....as with the one episode of 'Moon Knight' off of Disney + right now. So it must have been a fluke that you are able to now. Have you tried any other services because that is not how Streamfab works.
Down2Earth
Yep I have been using StreamFab for Hulu, Disney+, HBO, and Netflix. For Paramount+ I have used it for Seal Team and Picard just fine. The earlier issue I had with Picard was after Halo bugged the current running Streamfab instance but after restarting StreamFab then Picard downloaded fine.
I tried downloading Halo multiple times over multiple days....same result. It was not until today that it would download fine (after episode 2 had appeared). That is the only change this week and still using StreamFab 5.0.2.6 on Win10. So why it worked for you and not me is strange. Halo was the only issue I have ever had with any movie or TV show downloading thus far.
I just upgraded to 5.0.2.7 as of a few minutes ago since it is available.
Here is what the StreamFab downloader window would look like PRIOR to today...when there was only 1 episode. Did you have the same where it shows "Select All" but no Season/Episode list after?