My swim script has a float delay on it?

Here's how the beginning of my swimming script goes:

Humanoid.Changed:connect(function(Property)
    if not Root then
        return
    end
    if Root.Position.Y < WaterHeight then -- and not Debounce
        Swimming = true
        local BodyForce = script.SwimPosition:Clone()
        if not Debounce then
            Debounce = true
            BodyForce.Parent = script.Parent.HumanoidRootPart
            BodyForce.MaxForce = Vector3.new(0, 9e9, 0)
            Debounce = false
        end
        IdleController:Play()

for some weird reason, when I drop into the water I sink then I rise up really fast. I don't see this in any other games. Examples such as:

My Game: https://gyazo.com/fff02da83a89b6595d9b2fdddd3ce1a1

Other Game: https://gyazo.com/36bad857ca4b4c1ae0e5c8628c45ac92