Plugin name is same as class in NPC, it must be changed (or made main class private)

public class HumanNPC : NPCPlayer, IThinker
{
  public HumanNPC.SpeedType desiredSpeed = HumanNPC.SpeedType.SlowWalk;
  [Header("Detection")]
  public float sightRange = 30f;
  public float sightRangeLarge = 200f;
  public float visionCone = -0.8f;
  [Header("Damage")]
...
}​