Other than the case of defective material in the wipperman stainless chains, I've never seen a documented case of outer or inner plates breaking, but it could certainly happen. Most often, an other plate comes off the end of a pin.
Shimanao's joining pin is the most likely culprit, but when you have over 200 peened ends, the chances of one bad one increase. Older 7/8 speed chains were of the protruding pin design that had less chance of failing.
About shifting causing a failure - if you shift too late under a real heavy chain tension, the chain can get twisted and pull a plate off the pin. It might not occur at that moment, but later, so the cause is not obvious.