I did a quick search, but couldn't find anything so here goes:
When I try my app on a Sony Xperia 5 phone (21:9) aspect ratio, part of the screen is black and not used by the app. It doesn't matter what display mode I use, it's like that part of the screen doesn't exist.
I also tried different resolutions for 4:3, 16:9 and 21:9 but nothing works.
I'm downloading all the latest API updates on android SDK as I write this to see if it will fix anything, but it's taking a awhile, so I thought I'd ask you too!
Black part not part of app: