After having a known good backup; I would consider scheduling a downtime, shutting down the hosts, and doing a clean complete restart of the MSA by using the "restart sc both" and "restart mc both" commands. My guess is that you have some stale management controller data or other quirkyness caused by the 'failed' controller. Maybe a clean reboot will revive the failed controller too?
See https://h20565.www2.hpe.com/hpsc/doc/public/display?sp4ts.oid=4118559&docId=emr_na-c02520779&docLocale=en_US page 126.