Sharing this here since I've seen a few reports of it elsewhere and was impacted by it myself. Even though the game isn't "episodic" like Hitman 2016, each location is it's own download, including the Legacy Pack locations of Paris, Sapienza, etc. What happened to me was that one location appeared to download - it showed as owned in the Xbox store and downloaded under "Manage my games and apps," but the Hitman 2 wrapper wouldn't recognize it and told me when I tried to look at it from the Destination menu that I didn't have access and tried to send me out to the Xbox store. Uninstalling and reinstalling the episode in question (Santa Fortuna for me, Bangkok from H1 for others I saw) didn't work; I even uninstalled and reinstalled the entire game and still had the problem.

What did work eventually was this set of steps:

1. Uninstall the location that won't load.
2. Do a hard shut down of the Xbox One, holding the box's power button down for ~10 seconds until it turns off
3. Wait at least 30 seconds to turn it back on (I waited a few minutes, and even disconnected and reconnected power before doing so)
4. Power back up, and the "missing" location should redownload and be recognized. (This worked for me, the rest is advice from others who had to keep troubleshooting)
5. If it doesn't autodownload, you can go to My Games and Apps, press the Start button on Hitman 2, and choose "Manage Games and Add-ons" to select the episode and download it.
6. If the game STILL doesn't recognize the location as being installed, repeat step 1, but go into your settings and turn off all netowrk connectivity beofre doing the hard reset, and restore it after turning the console back on.

The situation was super frustrating for me, but once I found these steps it was fixed relatively quickly. Hope no one else runs into this, or that this helps someone else.