IphoneX like devices they use a 19.5:9 cause of the long screen, and basically most of the iphones are using a odd number as ratio, but if you doing android 16:9 should fit perfectly to all devices..... try to make your game targeting the screen aspect ratio and not the devices screen size.
on my testings i also see a blackbar when i load the app, but if i send it back to background and come back to it, the screen adjusts fine, i think might be a device issue or something changed in the code for Construct scale method.