Its Facebook Messenger and Facebook app. Huge battery hoggers both of them. I uninstalled them both and installed Friendly for Facebook app instead. Now I have around 15-20% more battery left when its time to put the phone to charge at night.
Holy ****, i uninstalled and disabled all facebook on my S8 and installed the Lite versions. Also of messenger.
I am now also getting 4% at night. Before it was a couple of percent per hour !