properly installed?
What I see in the photo is a gap between the d’Brake and the bearing housing. Did you loosen the screw before taking this photo or did you use the d’Brake with this gap? If you used the d’Brake with this gap, then this might probably have been the reason for it’s breaking. This would have terribly increased the tensile stress at the point where the crack started.
Does your frame have a plane surface at it’s lower side, respectively does it have machined bearing housings or such ones made of sheet metal? If they are made of sheet metal or otherwise offer no planar surface you’ll neet an adapter like Hugo or me did it here and here. Without the d’Brake being screwed gapless to a planar surface the brake force will not go into the frame as it should but will go over the whole d’Brake and into the bearing.