Thanks Sixsens,
So session-wise it is stable enough to play with without the players losing session or splitting off into their own session?
which bugs were definitely not in 2.8.3?
I saw that EnemiesCanSpawnPickups was not being enforced in the code, and that is fixed now.
Also, I see where /stop is affecting pickups not being cleaned.
I remember after your testing that I started spawning mission pickups like reward pickups, to be spawned on every client, since they were not being carried across to other clients like NPCs and other entities. This explains why the reco and deco player saw the pickup again. The pickup being picked up twice then disappearing… it sounds like there is some network awareness with pickups, if the other 2 players didnt see it, and
As far as everyone going offline and NPCs disappearing, I guess I am not surprised. At the least I can put in a check in the code to not give a reward if zero NPCs. Though I looked more into what Loque posted re: network aware resource manifest and network settings. I see that Fivem_Cops does an ObjToNet call and some other network related settings when stuff is created, which I will play about with and may add. This may allow the ownership of game objects to migrate properly to other clients if a host/spawner leaves the session. This may actually help with any session related issues that you may be experiencing as well, if you still are. Not sure if it will fix all NPCs disappearing when players disconnect.
It sounds like most of the problems are with pickups for you, not with NPCs,vehicles or plaeceables not showing up… at least when at least one player is connected? My big concern was spawning entities across the other side of the map from a player/players and them (including pickups) not being seen by players. So if all players are on one side of the map, and a mission spawns the complete opposite side, everyone can see blips and NPCs etc…when they get there? Same with players that have connected afterwords during the mission? They can see npcs and their blips ok?
Its possible that setting network ids for pickups (if possible) may help with your pickup problems as well. Thanks for the spawn coords tips as well.
For a test a while back, I updated to the latest resource manifest and spawned a prop in a mission. I had just logged in after starting my client, and teleported into where the object was from about 1/7th to 1/8th of the map away, and it just was not there. Same as if I drove there as well. Whereas if I was nearby it would show up. This might be solved by using ObjToNet and generating netids etc…during creation, though I am not sure. From what I have read, there is no guarantee that entities will persist for all clients at all times. Same with netids, they have finite values and are mutable since so many objects can be created during the session by players, that the game runs out of netids and recycles them. It make sense that GTA works this way, but may be bad news for truly persistent missions. Though, it sounds like your players have not encountered disappearing NPCs vehicles etc… for the missions, which is good news 
Thanks for the suggestions.
RE: Timer, yes, I had a build with a timer, but realized that it needed more work to have the server control mission flow better. Its something that I have thought of. Different missions types like the checkpoint one you mention is cool. RE: Melee weapon, that might be an easier one to add, by setting the ped combat attribute.
