Achievement "The Challenger" not unlocking?

Games Other Halo
1

I got my 25th Challenges completed today but the achievement didn’t unlock.

any idea why?

2

In the campaign mode I completed the chapter Infinity and I did not get the achievement for it. Also it doesn’t say I completed it where it shows the highest difficulty completed but I started the next chapter so it should show as completed … must be an issue with some achievements

3

I am having the same problem, Im now done with my 26th challenge and still no
achievement. Even checked my challenges on here to make sure and I have 26 done.
I look at my achievements, Nothing!

4

Strange that some of you guys are having this issue because i got mine when i did a 25th challange

5
6

Just keep doing them. Mine popped on the 27th or 28th.