Starcraft 2 is one of the games I've played fairly extensively myself while testing the app, and one of the most played games with the app, so I feel fairly safe in saying that this may be something else. I'm going to first ask to make sure you have all overlays for applications such as teamspeak overlay, mumble overlay, all completely off, and try again, because they will cause conflicts in the game. If you're using fraps or anything with OBS, shut it down, as it if you're using a graphics enhancer, please turn that off as well. If you continue to have problems you can also use window capture which should give you almost the same performance as game capture.
