Thanks for trying this in Co-op battles.
I would recommend to try these options first:
to close all unnecessary applications before the start of the game
delete modifications if you have any (you may also start game in a "Safe mode", check this with the right edge of "Play" button in WGCenter)
"check and repair" client via WGC >> Game Settings
(This topic may be helpful with the first two points)
delete your preferences.xml file in the game folder and set everything manually again with the next game launch
choose another graphic settings and check the result
And only if nothing works, then to create a WGCheck report and send it to our Support in the ticket with some notes. We'll investigate what is the reason.