I've got a couple devices using MKL26Z128VFM4s that have failed in a way that causes the uC to repeatably draw very large (>1A, given enough power supply) currents as soon as power is supplied. I don't know what events might have preceded the initial failure (they were out of my hands at the time), but I had two suspicions: floating inputs and a weak overvoltage on an input pin. The input overvoltage was limited to VCC+0.9V and could only have supplied about 50uA, and applying the same conditions to other devices for extended durations has not replicated the failure. There are also a couple unused pins, and I don't know what could have been going on with those. When the first one happened, I suspected ESD, but then a second one came back to my bench with similar symptoms so I expect it's something more deterministic.
Does anybody know what sort of conditions might damage a chip like that? I did find that if I supply enough power, in the brief moment before it gets dangerously hot, at least one of the KL26s still executes its code and responds to SWD.