Hi @TELCOM
Do you have a screen protector fitted or privacy screen protector as thesebcan sometimes hinder the sensors and screen ?
Your phone has diagnostic tools.
One is in your Samsung Members App under the GetHelp section.
The other is in your phone app when in the keypad typing in *#0*#
If no help then first try Safe Mode > https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/ turns off downloaded apps and themes etc which may highlight an app or theme that's causing conflict.
If the issues continues then assuming all your software is up to date as a last resort back up and factory reset.
If this fails to help then a Samsung Service Centre or Samsung Experience Store may need to look at it.
I wish you all the best. 
