I have four pis, all rev 2b running Raspbian, all connected to the same PSU. They're each plugged into ethernet, power, and HDMI, and nothing else (no GPIO, USB, etc.). I always run a soft shutdown. When booting them, by plugging the four-port USB PSU into an outlet, one of them stopped booting. The ACT LED does not blink, the power LED is bright and solid.
I've gone through the boot problems sticky, but none of it seems to apply. I've swapped all the cables, tried the SD from one of the working pis (it didn't work), and tried booting it without the other pis connected. I swapped in a fifth pi, using the SD from the non-booting pi, and the new pi works fine. I also left it for over a week without power, in case it was the polyfuse, but it did not come back up.
Is there anything else I can check in this case, or should I just presume the pi is bricked? Secondarily, what might have been the cause so I can try to avoid it in the future?
UPDATE: The new, fifth, pi is now in the same state as the non-booting pi. So there is definitely something going on with my setup. Could it be something on the SD, that wouldn't exhibit any other issues when plugged into another pi?