How does progression work While playing coop?

[Striker]

i've been playing with a mate and i swear whenever i pick up SHD caches in his game It's still there in mine? Also how does thios work for the main story missions

[CascadeHush]

If you have unlocked the prerequisite missions then doing missions should count for your own progression, at least it did when I played through the world tiers on Playstation.

I even had a situation where I went from world tier 3 to 4 at the same time my friend went from 2 to 3 because we did the final stronghold together.