They notification system is broken on Android!

You receive a push notification -> You open it and see the content -> Go back to the app's feed -> the app shows your notification as unread!

It happens every single time and I changed devices and it keeps happening, my current phone is a Nexus 5X. I honestly can't believe such a well known app has that kind of bug (You wont be able to convince me that that's not a bug and it's the expected behavior).