I played Halo SA at Windows RT tablet and I finished operation A. Then I installed the game on my PC using the same account and my progress is not loaded. I need to play the game from beginning. Although still, when I open the game at Windows RT I see operation A finished.
Were you connected to the internet on both devices when you opened the game and while you were playing it? Were you signed in using the same Windows Live ID on both devices?
I had the problem just today with my new Lumia 520 and the PC version.
I got it fixed by playing both games at the same time for a few minutes, after I went back to the title screen and it had synchronized in the meantime.
yes I was connected to internet when opening the game and while playing it. and I use the same MS account on both PCs.
it looks like the tablet was out of sync… when I reinstalled it (because of other thing), it downloaded game status from pc and now the progress is in sync, when I play it 
We’re glad this is working for you again, duracellko, and sorry for the delay in response. Please let us know if you run into any more trouble.