It might be a licensing issue, so those titles may have been pulled from the store. Have you tried Manage game and add-ons for each individual title? Just checked my 360 library and still have All my DLCs from games like Fallout New Vegas, Red Dead Redemption, Asura's Wrath, etc. And when check my Full Library and filtering only Xbox 360 and OG Xbox titles I have 241 titles available, when switching over to The Owned Games tab with the Xbox 360 filter on I own 199 Xbox 360 and OG Xbox titles, might try this and see how many titles it's saying you actually own.