PlatformStand not working 70% of the time?

I have this script where if you escape from a vampire that has grabbed you, the vampire has platform stand enabled for a short time to mimic stun. The problem is, it doesn't like working. Sometimes it'll work here and there, like if the player is in the air or not moving, but most of the time, it just doesn't stun the player. Is there a way to fix this?

progress.Changed:Connect(function()
            if progress.Value >= 100 and grabbed.Value == true then
                anim:Play()
                vampchar:WaitForChild("Humanoid").PlatformStand = true --heres where the stun starts
                local ff = Instance.new("ForceField")
                ff.Name = "FF"
                ff.Parent = v2
                spawn(function()
                    wait(1)
                    ff:Destroy()
                end)
                beast.Value = false
                progress.Value = 0
                grabbing.Value = false
                --grabbingwho.Value = ""
                grabbed.Value = false
                grabbedby.Value = ""
                vampchar.Head.face.Transparency = 0
                vampchar.Head.Decal2.Transparency = 1
                vampchar.Head.Red.Transparency = 1
                vampchar.Torso.Transparency = 0
                vampchar.Head.Transparency = 0
                vampchar["Left Arm"].Transparency = 0
                vampchar["Left Leg"].Transparency = 0
                vampchar["Right Arm"].Transparency = 0
                vampchar["Right Leg"].Transparency = 0

            end
            spawn(function()
                wait(2)
                vampchar:WaitForChild("Humanoid").PlatformStand = false -- and heres where it ends
            end)
        end)