I like Plexus but I don't count on it to clean anything more than a haze - I use it more as a polish. For heavily soiled windshield, soak with wet towels, then mild soap solution, then rinse, then dry, then Plexus. A lot of work while attached vertically to the bike. Sometimes I just remove the darn thing and wash it under a faucet.
What BlueStreak said. I hot-soak any bug guts or dried mud. Then use Plexus for the final clean and polish. You have to use a fresh section of towel (I use microfiber) for the final Plexus polish otherwise you have a little haze left.
Another recommendation for Plexus. I've had helmet face shields last 3-4 years. After every ride I wipe the bugs or grime off with it. It polishes the plastic surfaces so smooth the bugs clean up easier next time as well.
'06 Triumph Scrambler (Trans-Labrador veteran)
I've had very good results with a product from S-100 called "special surface cleaner". It comes in a smallish pump spray bottle & it seems to dissolve bugs better & faster than anything else i've tried & leaves the surface clear & slick. I believe S-100 products are in just about all the m/c dealers around.
I am a big fan of All Kleer. They make a product specific to motorcycles and you can buy it direct from the manufacturer. It is a GREAT cleaner and leaves some sort of a clear finish that makes it even easier to clean again. It is a product that has been widely used in the aviation industry for many years and is reasonably priced. I carry a bottle on the bike that I refill from the large 5 gallon jug in the garage.
In fact their Swirl Remover works extremely well at taking fine scratches out of plastic windscreens and headlight lenses, even the ones that have yellowed.
Some products are worth paying for; the Plexus I used was not.
Sounds like residue, best technique I have used,
Warm wet towels using nothing but water, let them sit
on windscreen for a bit to soften up the bugs, then rinse
them off well. No chemicals or soap and no residues.
Remember the last thing that goes through a bugs mind when it hits your wind-shield.....its azz