What things or scripts are notorious to create desync and lag?

Hi!
I run a FXServer with basically every esx script (more or less) and we have a bit of a problem with vehicle desyncing and voice crackling, and I was wondering what things and or scripts are notorious to create this desync and lag.
I do not believe it is my host that is bad as it runs on a Quad core E5 Xeon and 16GB RAM on a NVME drive.
It also has 1Gbit up and down, we do not have any custom scripts or something like that.