We have become aware of an issue with Xbox One users being able to claim their Ultimate Edition rewards. You will need to install the Doomsday Pack again. You should be able to fix it by doing the following:
1) Delete all DLC from your Xbox One;
2) Find the State of Decay 2 Ultimate Edition preorder bundle;
3) Navigate to the "In this bundle" section;
4) Download the DLC again from there.
Once it is reinstalled, launch the game and you will receive your jacket, combat helmet, and bonus prestige. Please submit a ticket if you are still having problems accessing the content once you have the Doomsday Pack installed again.