How are all these Cree LEDs damaged?
I found the problem.  After slightly moving each LED around on the aluminum plate, different parts of the LEDs flashed on and off.  The layer of copper that composes the circuit in each PCB is exposed at the edges, and was contacting the surrounding pieces of aluminum.

The LED that had a diagonal dimmer part was damaged by putting too much pressure on the dome.  I guess I'll just have to rip the dome completely off that one.