I had this issue come up a few times which resulted in a ban in competitive, because I had to restart the game: After experimenting a bit I found a way to reproduce the glitch:
- Have OW open
- Alt-Tab and start (specifically) Apple Music (desktop application)
This results in a flickering white screen, that makes it impossible to see anything. Restarting the game is the only option to resolve that issue. (changing the Screen Mode to “Windowed” limits the screen issue to the lower left corner)