I had this, tried uninstalling/reinstalling DLC, nope. Tried the same with the game, it worked. Closed game down while I did something else (about 30 mins), came back, same thing again. Both FH3 and FM7 not available for my account. Tried signing out and back into Windows Store, same with Xbox, still no joy. Finally, as a last ditch attempt to resolve it before having to uninstall, I decided to reset the Xbox app, and BINGO!
I haven't tried it again, as I haven't played since (because zzz), but will update if it happens again. It does seem to be an Xbox app issue though.
I could agree with you, but then we'd both be wrong