Make sure Halo 4 Reflow is selected in the Workshop tab under the MCC Properties in Steam, and it should appear in the Halo 4 campaign menu if it's fully downloaded.

.

every time i check the mod under the workshop tag, it unchecks it whenever i leave the tab and launch the game

It's doing the same for me, so I think that's a Steam bug; the best advice I can give is unsubscribe, and resubscribe to try kicking the download into gear.

i downloaded the full mod, but still getting the same issue

Did you guys ever find a solution to this? I'm having this problem now. I've tried un and re subbing to the mod to no avail.

It needed an update, which has been uploaded now.

same issue here, Reflow as working great before and now i can't get it to activate no matter how many times i re-sub.

IT WORKS! Thanks, saw the tiny update got downloaded while i was asleep. That was fast. Love to see such an active creator!

Can't seem to get this working unsubbed and resubbed, I then quit the whole game and loaded back into it and nothing worked kinda wondering what i'm doing wrong

Make sure you are running MCC with anti-cheat off: https://support.halowaypoint.com/hc/en-us/articles/360037475251-How-to-Launch-Halo-The-Master-Chief-Collection-with-Easy-Anti-Cheat-EAC-Disabled