This was the reason I stopped using it. It never kept track of my runs/daily walking etc..... I did have the background sync on (like you), but it didn't help. Then one day for no reason it started to work again and that's why I'm now using it again.

Try plating around with your permission settings on your actual phone and not the app. That might help. For me, I always though that once my phone went in to stand-by actifit stopped recording.

P.s. Use the tag #sportstalk when posting actifit posts and pick up some extra tokens.