Originally Posted by
Shahmeer Shahid 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.
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.