I first started playing halo Spartan assault on my windows phone when it first came out but only completed operation a and some of operation b because I found the controls to hard on a small screen. Then I purchased the Xbox box version and completed everything and unlocked all the achievements apart from the extra credit achievement until you released a update to fix it. Now my problem is I have now purchased the Xbox 360 versions and competed everything in this version but after several updates still can’t unlock the extra credit achievement. I think my problem could be caused by the assault ops challenge sidearm slaughter has over counted because so far I’ve done 450 kills with the magnum when it says I only need 50. The other thing I’ve noticed is it says 89 / 90 completed mission specific assault ops competed but I checked and redone every other assault ops mission so could you please help me because I’ve can’t think of anything else to try.
I believe that it is perhaps an account bug? Have you tried clearing your systems cache or re-downloading your profile? I have seen those fix these types of issues before.
Unfortunately, this is a known issue, the Counter Glitch. I attempt to summarize known information here.
There is a decent workaround for Xbox One, explained in the first post. But for Xbox 360, the only known workaround would be to redo every Assault Op while playing offline, then unlocking the achievement offline.
I suggest you post in that thread to continue to show 343 that this needs a real fix. A simple stat check on the server side should do it.