Co-Operation Weekly Challenge not progressing

A friend and I are playing split-screen co-op on Xbox One, in Halo 3, and even though we have completed a few levels so far, neither of us are receiving progress toward this challenge. Nothing in the challenge description indicates that this should be happening. We are using two non-scoring skulls on Heroic difficulty, but nothing other than that. Any suggestions/fixes/clarifications would be appreciated.

Never mind, it randomly decided to start working after one more level. No idea why, nothing changed…