Colt Element Rim Crack

During the first training day of YalgoraRace Enduro 2016 my Colt Element 27.5 rim had failed. I didn't have any crashes and I didn't hit the wheel much. I've noticed a crack when I was putting a bike in my car.

Maybe there was too much spoke tension..  A day before, I've managed to put 2-ply DH tire Maxxis HighRoller II with a steel bead on my rear wheel. It was so hard, and after this all the spokes have got unstrained. That's why I've taken a spoke key and made spokes strained again.

I have two wheelsets for my Norco Sight, so there were no problem in searching the wheel for the race.
In spite of the rim fail, I like Colt Element rims. They are very strong with a weight of only 435gr. Now I know, that I need more heavy rim for my rear wheel on an Enduro bike.