Unclear sprayhood isinglass must be replaced

There is something on my acrylic windows in the sprayhood, it seems like it is a kind of algae or a coat of dirt, but why is it only on two of the windows ? In this video I try to clean the acrylic glass with a product there is made for cleaning windows in sprayhoods. The product does not do anything so I switch to a bit more powerful product from Starbrite with a bit more kick.