I have also come across this problem...
C2 on some occasions seems to lag, if I click the action or event box there is a 1-2sec delay before it opens, if I start typing in an input box there is around a 1/4sec delay between each letter appearing on the screen.
I then have to minimize C2 and maximize it to get it to return back to normal.
Unfortunately I haven't been unable to find the cause of this problem.
It isn't connected to the size of the project either, only yesterday I was making a small prototype game approx 20 stationary sprites and 60 events and had the same problem...
At least the minimize maximize trick works