At certain times of day and regardless of any specific lighting settings, changing the lightings ClockTime / time of day across specific time windows will cause clouds to generate scrolling visual artifacts.
I do not notice this issue with a the escape menu graphics quality set to under 3, but it is present at every level above it.
To repro the video above, open a brand new place (ctrl + n), and run the following code
local lighting = game:GetService("Lighting")
local tweenService = game:GetService("TweenService")
local clouds = Instance.new("Clouds")
clouds.Cover = 0.7
clouds.Parent = workspace.Terrain
local info = TweenInfo.new(10, Enum.EasingStyle.Linear)
while true do
lighting.ClockTime = 5
local tween = tweenService:Create(lighting, info, {ClockTime = 8})
tween:Play()
tween.Completed:Wait()
end