You can get that sort of congestion happening in Solo too - it just needs there to be enough NPC ships about that they get in each other's way, and for you to leave the instance running long enough. Jaques Station where it gets a lot of Belugas from the nearby tourist beacons trying to use the slot regularly jams up without needing more than a player to observe it: eventually what happens is the queue to progress through the slot gets so long that the ships on the inside exceed the departure timer and get shot down ... then the wreckage from that drifts into a position where it blocks something trying to get in through the slot, and it escalates from there.
Certainly easier in PG/Open, both to have the instances last longer and for CMDRs not on docking computer to mess up the traffic control routine.
