Halo ODST not unlocking

I bought the Add-on but the game does not recognize it. When I try to start it it says that I have to purchase it. When I go to the installation details it shows me that the content is installed and the size of the installation is right (bigger than the regular MCC). The page in the MS Shop shows that I bought the add-on. I tried to delete and redownload it. I even redownloaded the whole MCC, but nothing helps. Any ideas what is going on?

[deleted]

Sorry for the late reply but I was away from my console for a while. I just checked and it is listed as installed (showing 10 mb).
This is really confusing. I have no idea why it refuses to launch.