There's a thread about this here:
https://forums.forzamoto...dating-on-Forza-hub.aspxbut it's better if it's reported here in the support section.
As far as I can tell, the achievements are registering, and can be seen in the hub app, but gamerscore isn't updating in the rewards system. This is also the case for other games, I've been getting achievements in FM7 and FH3 without the points for gamerscore updating in the rewards system.