Marshmallow update causing havoc

[ekendraed]

I have updated my S7 edge to Android 6.0.1 and now WhatsApp does not show contacts by name from my contacts page.
I get this very annoying message to ALLOW or DENY apps with TURN OFF SCREEN OVERLAY from settings >apps and I don't have a clue what to do.
I am unable to work VIDEO on Skype.

Is there any way to roll back to the previous Android version?

 

[ekendraed]

Problem resolved after removing DU BATTERY SAVER AND CCLEANER. I don't have CM.
After that I was also able to allow WhatsApp to access my contacts and now instead of numbers I have names.
Credit goes to a guy who posted the info on utube