I’m not sure why this is. But under the “games won” section it only counts games won on Infinity Slayer. It doesn’t count anything else. I have played 70 games, lost about 5 of those. I should have 65 games won. But alas I only have 21. For the monthly challenge as well it says 21/117. I’m sure this is happening for other people as well. Every win no matter the playlist should count! I’m really enjoying Halo 4 but this little thing is annoying!
Edit: Sorry for caps.