2 monitors: 1 - 144hz 1080p, 2 - 60hz 1080p
Game is running in Windowed Borderless

Steps to reproduce:

  1. Monitor 1 is running the game, Monitor 2 is running Google chrome with several tabs, including Youtube/Netflix.
  2. Search for a regular PVP game.
  3. ALT + TAB to Chrome and stream a video at 1080p.
  4. Once you see a game has been found, ALT + TAB back to the game window.
  5. Observe.

For a few seconds player sees very large stuttering/streaming issues, frame loss.
(I have 100MB Broadband, my guess is this is PC/Game side lag)
Unable to select a team, including spectators, options will either be greyed out or not present at all.
Pause Menu otherwise still works, however you are completely unable to get into the match.
Only 'workaround' is to Pause Menu > Leave Game then matchmake again.

This does not reproduce consistently however the steps above are the best I have based on experience.