This is probably due to you matching up against more remote players. Where are you based?
We are working on a fix for this. Hopefully available next patch!
I'm located in Denmark, so just North of Germany. But might be an extreme case due to me playing at odd hours.
The simple fact you stated yourself saying that only 1/3 of games are laggy proves that's not general.
Chances are it's a matter of geographically remote players.
Well could be general issue that the matchmaking would match people with horrid connection to each others at a whim. and "only" 1/3 of game is a high number all things considered. That's 1/3 of the games being where i just have to surrender at start as i really don't care to play them.
Were just suprised to get almost instantly matched up upon queue to then enter games that were bordering on unplayable. As you wouldn't expect the matchmaking to crete such a match without first waiting some time while looking for games with playes in closer proximity.