Dear oh dear, do IBM ever learn?
This just sounds so familiar.
It's been about 7 years and 2 employers since I last had anything to do with a DS8000 series (in Open Systems, not Mainframe), but even then there were Microcode bugs a-plenty. One resulted in 2 days of downtime for services that generated a lot of revenue, due to a bug which incorrectly failed several disks in a single RAID Group. I think it was also a known bug, but we weren't informed early enough. And they also had a script to handle sparing differently, which we received afterwards.....
After this outage and subsequent roasting, IBM were a bit more pro-active in reporting potential problems.
Seems the lesson was not learned, or failed to make it across the pond.