The Finder/Get Info checkmark for preventing App Nap sometimes disappears, seemingly at random. Maybe the app updates itself, or just writes something to the application directory and the checkmark is gone. The next day your overnight render is at 10%. So in Terminal, type:This seems to prevent App Nap completely, looking at the Activity Monitor » Energy » App Nap column. Running programs need to be restarted for the change to take effect.
Mac OS X Hints