Why does third person make my character go through walls?

I have a problem where everytime I go third person in my game I can walk through walls as long as I am not jumping.

Here is a video of what is going on: https://youtu.be/x01zF-RkdSs

Here is my script for third/first person.

USER_S.InputBegan:Connect(function(input)
    local key = input.KeyCode
    if key == Enum.KeyCode.Z or key == Enum.KeyCode.DPadUp then
        local player = game.Players.LocalPlayer
        if player.CameraMode == Enum.CameraMode.LockFirstPerson then
            player.CameraMode = Enum.CameraMode.Classic
            game.Players.LocalPlayer.CameraMinZoomDistance = 2
        else
            game.Players.LocalPlayer.CameraMode = Enum.CameraMode.LockFirstPerson
            game.Players.LocalPlayer.CameraMinZoomDistance = 0
        end
    end
    if key == Enum.KeyCode.ButtonR1 then
        autodown = true
    end
end)