For people having issues with the phone's display staying in sleep after moving it away from your cheek at the end of a call. I may have found the solution. This took me a while to troubleshoot.
There seems to be a problem when What'sApp contacts are synced to the phones address book. Choose not to sync your What'sApp contacts and hopefully this will fix this issue for you. It did for me anyway. I believe it's when you have a contact with a saved number to the phone or sim etc... and also a What'sApp contact number saved to the same person. It must be a bug in the phone's software/app.
I hope this helped you all.