I know you said that NPC spawns were/are still a new thing but while using this to spawn a few around the map certain monuments (oxums gas station & dome) caused incredible FPS drops when even slightly near them, disabling the profile for each fixed this for all but one of the gas staions which remains to be a FPS killer, all the way down to 5FPS for some players.

Can you share the steps to reproduce the issue? Best way is to share a profile that I can just install to see the issue.

Ive included both problematic profiles

https://pastebin.com/sdtAJPJd

https://pastebin.com/zwsumZBG

Cool thing about this plugin is I can just install those profiles with a command like mainstall https://pastebin.com/raw/sdtAJPJd.

I tested both profiles and saw no client FPS drops when enabled. For Dome, I was seeing a constant 75-85fps before and after enabling the profile. For Oxums, I was seeing a constant 90-100 FPS before and after enabling the profile. I tested both with the nav mesh disabled and again with it enabled. I tested in vanish as well as outside of vanish with the NPC targeting me.

Can you try spawning the NPC prefab (scientistnpc_full_pistol) via the spawn command in the F1 console to see if the issue happens then? The plugin doesn't do anything particularly special when spawning the NPCs except set their desired nav mesh area to Walkable instead of HumanNpc, in order to allow them to navigate and to avoid console errors. That should only be relevant server side, so I can't think of any reason why spawning these NPCs would reduce client FPS that much, nor why the FPS drops would remain after removing the NPCs. That suggests to me that the FPS drop was probably caused by something else.

Oh cool didnt realise it would install from a pastebin link!

I have spawned it (scientistnpc_full_pistol) via console and it seems to be fine, also another profile is using that prefab with no issues. The reason I think it was this plugin is due to the fact the only areas affected by the drops were ones with these NPC's spawned and as I mentioned when I had disabled the profiles all but one area was fine afterwards. 

Thank you for trying anyways!