A year or two after that I had an M4 that after a certain period of uptime would just stop responding to commands, thus acting like a dead drive until power cycled (a reboot was not enough). There was of course a fw update available and it did fix it, although I don't recall it being listed in the changelog.
It killed a whole fleet of processing unit in our lab back then which had been all put in service at the same time, ran 24/7 and then failed all within the same night.
