For some reason lately (i guess after upgrading Unity?) start not to show full screen on Samsung Galaxy S8 using Portrait mode (2220x1080).
No sure how it happens.
In my player settings → Resolution and Presentation → Aspect Ratio mode is set to native aspect ratio.
As it is device specific, I couldn’t handle it from unity, however, on the device if you go to settings, display, full screen apps; and enable your app, it should appear properly.