player slides after pressing left shift?

i am making a custom character

the tittle only covers part

when i press w it goes forward

then i press shift to run it works

i then take my finger off of shift and the play slides for a sec then starts walking normally

• sorry for long code *

game.Workspace.Camera.CameraType = Enum.CameraType.Attach
local UIS = game:GetService("UserInputService")

local animations_folder = script:WaitForChild("animations")
local player = script.Parent
local humanoid = player.Humanoid

local jump_forward = animations_folder:WaitForChild("jump_forward")
local run = animations_folder:WaitForChild("run")
local left = animations_folder:WaitForChild("left")
local forward = animations_folder:WaitForChild("forward")

local jump_forward_anim = humanoid.Animator:LoadAnimation(jump_forward)
local run_anim = humanoid.Animator:LoadAnimation(run)
local left_anim = humanoid.Animator:LoadAnimation(left)
local forward_anim = humanoid.Animator:LoadAnimation(forward)

local positions_folder = script.positions
local head_pos_value = positions_folder.head.Value

function input_started()
    if UIS:IsKeyDown(Enum.KeyCode.Space) and UIS:IsKeyDown(Enum.KeyCode.W) then
        jump_forward_anim:Play()
    end
    if UIS:IsKeyDown(Enum.KeyCode.A) then
        left_anim:Play()
    end
    if UIS:IsKeyDown(Enum.KeyCode.W) then
        forward_anim:Play()
        humanoid.WalkSpeed = 10
        run_anim:Stop()
    end
    if UIS:IsKeyDown(Enum.KeyCode.LeftShift) then
        if UIS:IsKeyDown(Enum.KeyCode.W) then
            run_anim:Play()
            humanoid.WalkSpeed = 20
        end
    end
    if UIS:IsKeyDown(Enum.KeyCode.S) then
        forward_anim:Play()
    end
    if UIS:IsKeyDown(Enum.KeyCode.D) then

    end
end

function input_stopped()
    left_anim:Stop()
    forward_anim:Stop()
    run_anim:Stop()
end

while true do
    UIS.InputBegan:Connect(input_started)
    UIS.InputEnded:Connect(input_stopped)
    wait(0.1)
end