I wasn't sure where to put this, so I picked other. Me and my friend are playing a server, and I managed to get a lot farther ahead of him, so its kinda frustrating that he has no reason to do missions now, since I unlocked everything, I don't mind most of them but the mysterious trader one bothers me, since upgrading weapons is the reward for completing the game, and you don't actually need to do the missions to get the gear to do these Gates.
Solutions: Play missions despite having that unlocked. Missions are fun and they progress the story for that individual character too. If you plan to play multiplayer with another person, don't play without them. It's more fun to progress together as a team rather than separately. Reset the mission progress in the universe