I’m on an iPad Pro, not an iPhone. The Notification Flag won’t disable despite viewing ALL the notifications. It displays ON, and doesn’t clear the “Flag.”
We are planning to fix this as follows: Arrival of a new notification will set the flag to "1", opening the app will clear the flag. We are going to be relying more and more on the built in Notification Center as the go to place for notifications, especially taking advantage of the "group notifications" feature which was rolled out by Apple in iOS 12.
Customer support service by UserEcho