"Car Culture" achievement not counted by the rewards program

I am pretty sure, this is a “one in a million” thing, let me explain:

Sep. 11th I unlocked several achievements, “Car Culture” was one of them.
Problem: When the achievement unlocked, I just pened (snapped) the achievement app (to see how far my Ferrari progress went).

In the upper left corner of the dashboard you can see your last activities (start game, party invites, achievements and so on).
But the achievement was NOT shown there. The achievements unlocked earlier and later were shown.
My gamerscore did rise 50G, the achievement is unlocked in my profile, in the reward program’s achievement list, on xbox.com and on trueachievements.com

When I unlocked it back then, I had 750 G in Forza 6. The reward program did count 700.
When I reached 900 G, the reward program counted 850 and when I “finished” the game with 950 G (World traveler still missing ;)), rewards does count 900 G.

So I am missing 50 G since this app snap mistake(?) happened - till today.

Is there anything I can do?
Or shall I wait for the first DLC (maybe a track or the Porsche pack), get 50+ G there and then have 1000+ G in my rewards program? // Does this even count or work this way?

Thanks for your time,
Joerg (KO771)

So, after getting my last 50 Gamerscore (World Traveler) yesterday, my rewards have updated and are still the 50 G short that should have been gained by “Car Culture”.