I think I have some problem with the display. 1) When I touch the fingerprint scanner to unlock the screen or an app the display change its contrast or something like that. 2) Whenever I scroll down (or up), I get this kind of purple drag, but this is only visible with black images. 3) Overall the screen quality seems poor on low brightness, not uniform and with a strange textured feeling on gray colors. Am I the only having trouble with these problems?
totally normal. All phones does this to improve performance during reading your fingerprint could be some amoled lag that you're experiencing If you mean at very low brightness then this is completely normal too and it can be duplicated with any AMOLED display. Maybe you're used to using a phone with LCD display?