Ammonia! Thats it! There might be something else, i dont know...but i knew there was something in certain cleaners to ruin tint. Most products will say "tint safe" but if String knows what works follow that.Any of the car glass cleaners are fine. Just nothing with ammonia. Thats a big no no. I use basic rain x spray on both the inside and outside of our car. I only use microfiber towels too.
Been using the same stuff for years on previous cars.
Just stick with nothing with ammonia and micro fiber towels.