Sometimes the end-of-mission loading screen can take too long, especially for players with a poor/slow internet connection, and cause the player loading out of the previous mission to be dragged into the next when another squadmate force-starts the timer for it.
My proposed solution is to disable force-starting the next mission for as long as anyone in the squad is still loading out of the last mission. This will prevent a lot of annoyance on all sides and help players gain some more control over what missions they join.