It also happened to me on a Ubuntu x64 laptop
I started using Gravit Design yesterday (3/1/18), and download the night before, the link says v=3.2.7, the app splash screen says 3.2.6
The screen got blank today, and let me just the top bar when it was maximized. Then i unmaximize the program, and since it overwrites the Ubuntu’s bar and buttons, i became full blank and there was no button to even close the program. I had use the system monitor to force quit it
It also blinks a lot in imprevisible moments.
I think it is a problem with the graphic card