I updated to Volla 12.1 and had a flashing screen that didn't stop.
To fix this do the following (note that the flashing can continue between steps; simply go back to the drop-down menu and you should find yourself at the step that you have already reached):
drag the menu from the top of the screen
go to settings
go to apps
go to see all ** apps
go to Volla
go to Storage and Cache
CLICK ON CLEAR STORAGE
It should stop. It did for me at least