How could our sliding mirror doors have cracked so easily?
The main problem is that the energy that is stored when you open and close the doors are delivered direct to the mirror and the frames, cracking the glass or the wood. Check to see if your installation was done properly. Also, if you don't want to go through problems with the manufacturer, you can try to do some wood work and reforce the frames. Try not to hit the sliding dors when opending and closing them.

Hope it helps!