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)