It would be a good idea to capture the Intel System Information Retrieval Utility logs to learn what’s being recorded when this issue occurs.
It was not noted in your comments but in case is needed the most recent firmware for the RAID controller is 23.33.0-0022.
Are there any other cards installed in the system?
Thanks for looking.
Yes, realized everything was older than I thought...have downloaded updates and will try to apply - soon - before next 'update Tuesday'...
With luck won't screw something else up...