Here's the specific log:

[185939] Current screen dimensions of 3440x1440 are not an allowable ratio (2.388889) so we are forcing windowed mode.

I see threads about this issue so I'm just another drop in the bucket but I mean come on... the game looks great with 4k and it plays fine during matches and on the menus, however I'm guessing there's one specific scene during the match transition that doesn't allow that ratio so this is what we get...