I have the same issue on my SGS2 (GT-I9100). I only bought cogs after the upgrade to 4.0.4 so I can't tell whether the issue is due to the firmware or not. I had trouble with other apps after the upgrade, such as androidify giving a force-close right after starting it, but I could get rid of them with a factory reset. Cogs still has the same issue.
After some time the game freezes the phone completely. It doesn't react to any buttons and keeps producing the sound it was making when the freeze occurred. A hard reset (5 secs on power button) is necessary.
There was no obvious action that immediately preceded the freeze so the issue can only be reproduced by using the app for 5-10 minutes normally.
I used logcat but there were no messages related to the freeze or cogs.