Hi,
when I am in fullscreen mode, if I split the screen to use Artstudio and other app together some of the buttons in the top bar disappear. I have seen the layers button and the fullscreen button gone.
This is pretty consistent in an iPad 9.7" running the latest version of iOS and Artstudio 1.3.6. The steps to reproduce it:
1.- Enable fullscreen
2.- Open a second app in split mode in portrait
3.- Close the split mode keeping Artstudio
4.- Check the buttons in the top bar.