Accumulated dust & debris on the surface of any plastic can cause scratches of varying severity, it's important to gently remove that before attempting to clean your plastic windows.
Compressed air or if possible a gentle spray of water tends to wash it away---not sure if the Plexus would be compatible if the window was wet.
As most probably already know anything even slightly abrasive affects the surface so keep that in mind when choosing your cleaning products and wipers.
BTW Plexus sounds darn near for this sort of use!