Portrait format have control buttons misplaced over the song's cover as compared to README's screenshots
See screenshot below for where the buttons are placed on my phone. This happens whether the song have a cover or not (I just ended up using the same screenshot as the color scheme issue).
Screenshot
Device details: Xperia XZ running Android Oreo (8.0) on stock ROM.
I think that this issue is due to how I manage the disposition of elements on the player view. I will try the application on screen size like your phone on an emulator.
The latest version of the app has a better handling of small screens and this issue should not happen again (tested on an emulator with Android 8 and the same phone size as your Xperia XZ (5,2'')). Let me know if it works for you
This is indeed fixed.