Same thing happened to me on CMFB. Game is fine for about 40 minutes of turns into an hour and fifteen minute "Quick Battle". I press start to start my next turn and the entire game dumps and I go to my home computer screen. I have a Mac running OS X El Capitan, Processor: 3.2 GHz intel Core i5, Memory: 8GB 1600 MHz DDR3, Graphics: NVIDIA GeForce GT 755M 1024 MB.
Arthur