Is this the trick? Because I don't have any of the issues described by other players.

There is the occasional AFK/Farming player, most of them still show up when it starts. Though, for whatever reason, there's frequently an AFK player in Encampment/Survivor missions. Only encountered sabotage once, and it was presumably someone else using their account as they were 131 and still demanding weapons.

Typically the mission will start, everyone scatters to look for the objective. Usually someone will activate boosts (Movement/Energy). If the objective allows, trap tunnels go down in all four directions.

Once the objective starts, most players will hang back behind the tunnels, only peeking over the wall to spawn gadgets. Bruisers kill what makes it through the tunnels, Snipers shoot randomly through walls. Lobbers, Flingers and mini-bosses are really the only thing that will grab everyone's attention.