I have samsung galaxy A5 2016 and after updating it to the latest android security patch the "apps that can appear on top" is not working anymore...messenger's chat heads doesn't pop up anymore same with other apps with that feature and even tho in the notification bar it says "Chat heads active: 3 conversation" there's no chat head showing... additionally I enabled all the settings for "apps that can appear on top" but it's still not working I even reset my phone on its original factory settings for the second time around.
You may toggle on the Smart Pop-up View from the "Settings">"Advanced Features" and then choose which app you want to pop-up when receiving any notifications. If that doesn't work for you, then you can go to the "Settings">"Apps" then choose the app that used to pop-up, and scroll down. You will see a permission called "Appear on top". Toggle it on if it is not.
