Flag Grabs and Ball Blasts challenge is fixed and working again now.
I was notified by Halo support and gave it a try, progress is now counting and after 5 matches completed the challenge.
Just thought it worth a mention.
Edit: First post edit whoo 
Quit and restarted your game not just suspended and resumed it?
Playing Social, choosing Flag and Bomb game type?
Well I played CTF two days ago and it didn’t work. Then played another today and it didn’t work. But then I restarted again and played another CTF and it worked. Gonna see if it works twice in a row.
Ayyy looks like it is fixed. Literally started working as soon as I posted the first comment. Of course as soon as I complain about it, it starts to work again.
I enjoy it, though I really don’t care for XP progression, it’s jus reassurances that you’re helping out your team in different ways. I got all mine done in the MLG Reach playlist