The buttons in the Android app are invisible

[mobluse]

Describe the bug
There are no visible buttons. Only the calculator screen is shown and outside of that there is only a gray area. If I press the gray area I can hit the invisible buttons.

To Reproduce
Just start the Android app and you directly see it has no buttons. I have used an app to free the memory before I run it so it should run with maximum free RAM. I also used an app to shutdown all apps running in the background.

Expected behavior
The buttons should be shown.

Screenshots
I took a picture with a camera:

Desktop (please complete the following information):
Android, downloaded from Google Play June 13 2021: https://play.google.com/store/apps/details?id=io.github.omega.simulator
Version: 1.22.1 (March 21 2021).
My phone has Android 4.1 and is a Samsung Galaxy Fame Lite GT-S6790N (2014).