I started playing the 360 version of Halo: Spartan Assault on my Xbox One as a backward compatible game. I unlocked achievements, but when I went to check GTN & TA there were no updates. I then went to check what my gamerscore was on my console and it reads zero for the game.
Anyone run into any issues like this before. This is kind of the first BC game I have played on the One.
Haven't experienced the exact issue, but can say that sometimes there are delays in what your live profile says versus the reality. Then there is the sync/scan delay for GTN & TA. I played a few games yesterday that took until today for it to reflect properly in my profile on my console (but GTN showed as correct).
I also have issues of games not syncing between different platforms --- all unrelated from your exact question/issue.
The only BC game I've played recently was Bolt and it sync'd most achievements immediately. Give it an hour?