[PATHFINDING] My NPC is bugging out with runService.Stepped?

local npc = script.Parent
local head = npc:FindFirstChild("Head")
local debris = game:GetService("Debris")
local screamSound = head:FindFirstChild("ScreamSound")
local Zone = require(game.ReplicatedStorage.Zone)
local playersInZone = require(game.ServerScriptService.PlayersInZone3Script)
local container = workspace:FindFirstChild("RegionPart3")
local zone = Zone.new(container)
local npcTorso = npc:FindFirstChild("Torso")
local pathfindingService = game:GetService("PathfindingService")
local quickSlash = npc.Swing
local quickSlashAnimTrack = npc.Humanoid:LoadAnimation(quickSlash)
quickSlashAnimTrack.Priority = Enum.AnimationPriority.Action
local properties = {["WaypointSpacing"] = 1.1,
    ["AgentRadius"] = 2.5
}
local runService = game:GetService("RunService")


function getClosestPlayer()
    local closestPlayer, closestDistance = nil, 200
    for i,char in pairs(workspace:GetChildren()) do
        if char:FindFirstChild("Humanoid") and char ~= npc then
            local hmr = char:FindFirstChild("HumanoidRootPart")
            if hmr then
                local distance = (npcTorso.Position - char.HumanoidRootPart.Position).Magnitude
                if distance < closestDistance then
                    closestPlayer = char
                    closestDistance = distance
                end
            end
        end
    end
    return closestPlayer, closestDistance
end

function moveNPC()
    local path = pathfindingService:CreatePath(properties)
    local char, distance = getClosestPlayer()
    if char then
        path:ComputeAsync(npc.HumanoidRootPart.Position,char.PrimaryPart.Position)
        if (npc.HumanoidRootPart.Position - char.HumanoidRootPart.Position).Magnitude >20 and (npc.HumanoidRootPart.Position - char.HumanoidRootPart.Position).Magnitude >22 then
            screamSound:Play()
        end
        local waypoints = path:GetWaypoints()
        for i, waypoint in pairs(waypoints) do
            local part = Instance.new("Part")
            part.Size = Vector3.new(1,1,1)
            part.Transparency = 0.7
            part.CanCollide = false
            part.Position = waypoint.Position
            part.Parent = workspace
            debris:AddItem(part,.5)
            if (npc.HumanoidRootPart.Position - char.HumanoidRootPart.Position).Magnitude > 2.2 then
                npc.Humanoid:MoveTo(waypoint.Position)
            end
            while true do
                local distance = (npc.HumanoidRootPart.Position - waypoint.Position).Magnitude
                if distance < 5 then
                    break
                end
            wait()
            end

        end
    end
end

--[[zone.playerEntered:Connect(function(player)
    table.insert(playersInZone,player)
    print(player.Name.." entered zone 3")
end)

zone.playerExited:Connect(function(player)
    local playerFound = table.find(playersInZone,player)
    wait(0.5)
    table.remove(playersInZone,player)
    print(player.Name.." exited zone 3")
end)--]]

while wait() do
    --for i,player in pairs(playersInZone) do
    --  if i == 1 then
            runService.Stepped:Connect(moveNPC)
        --end
    --end
end

https://i.gyazo.com/cf2e7eca61d5f5f6f99e6ec9d615e889.mp4

So the NPC is walking towards the closest humanoid in a maze, however he seems to be bugging out (refer to gyazo link). I notice this only when I use runService.Stepped. If I just use a while loop, it doesn't happen however it doesn't follow the character smoothly, so I want to use runService. It seems to be moving back on itself, like as it it's trying to move to a previous waypoint for a split second. Anyway, if anyone can help I'd appreciate