TBH Been kinda looking a project to get into. Messing around in Unity and Unreal engine is fun but I am no skilled 3d artist. Just in the last few months have I gotten myself in blender and meh. Funny thing is I found this just looking around for a basic boilerplate c# project just to peep the api.
Admittedly I know squat all about FiveM (last played a few years ago when overall sync was still rough) I will have to check on the ped stuff to even see if what I am thinking is going to fix the desync problem.
[Edit] According to this thread I think my solution might be right. Anyone know how to create/manage peds on the server-side?
Looking at the script again I would seriously just try and make zombiemanager just a single server module. Just by a quick guess prob just have to change how you get the nearby player id to the distance checks to the zombie.
[Edit 2] Also if this uses OneSync you might be able to have a StreamIn and StreamOut method/Event which can really reduce overhead again this is just a rough guess documentation is really lacking on the api.