Just wanted to add and say that I haven't experienced this and I have a screen protector on my phone. I love that the touch sensitivity isn't affected by the protector at all.Lumia 640 is sort of like lumia 535, in the sense that it doesn't have an oleo-phobic coating. Maybe adding a screen protector especially a matte one and making a habit of cleaning of smudges on the screen might help since these are sweat smudges from your fingers and they interfere with the touch input.