Why do I not own Halo Master Chief collection anymore?

Hello chrisgerrad1,

Thank you for confirming. Halo: Combat Evolved does require Halo: The Master Chief Collection in order to play. Combat Evolved acts as an add-on of sorts for the Master Chief Collection. You will need the full purchase of the Master Chief Collection in order to own all the titles within the package.

I hope this helps!

-Tali

Halo ODST for the Xbox One is an Add-On for the Master Chief Collection. you must own that in order to play it.

When you fire up the Master Chief Collection, you should be able to start a campaign (under Halo 3) for ODST.

Halo 3 is part of Halo: The Master Chief Collection which consists of Halo 1 - 4.

https://www.microsoft.com/store/p/Halo-The-Master-Chief-Collection-Digital/BRNVR30J0SJ2

Anything you own will show as owned in the Xbox store or appear in your purchase history. If you can't find the game then it means it's not owned by your account and was most likely redeemed on another one.

I had something similar happen to me with a game called Marble Blast Ultra for Xbox 360. It's not possible to know why it was removed in your particular case, but for me it was because I had the hard drive replaced and the game code that I had used was associated
with a very specific hardware configuration that was set up when I first installed the game prior to replacing the hard drive. I had to call Microsoft support and explain the situation, confirm some information, and they provided me with a new redemption code
to reacquire the game. After getting the situation figured out, it now appears that the game license is associated with my gamertag/Microsoft account and I seem to be able to redownload it on new devices without issue.