Yes, the Android app is different from that perspective. In the iOS app, you can modify the device name, from the mobile app. On Android you have to change it from the hub, then log out and log back in picking the new name. I have a SM- too That's why I said they are "different".
Just remove all mobile phone devices from the hub, first, then create a new device. It will be called the same thing again, but once created you can change its name from the hub. If I were to guess, you probably created multiple devices and you are trying to send the notification to a previous iteration. Only the most recent device works. All others are no longer working.
Go to the hub's interface, click Devices, then remove any and all SM-N986U devices, then go to the app and under Settings select Hub, pick your hub, then select Create New Device on the bottom of the page.