Also, if the fault is in the drive itself I'm not sure it would work.
But that takes so long I'd like to avoid it if I can. I have an external Time Machine drive with a recent backup, so I guess I could attempt reformatting the OWC drive, installing High Sierra, then restoring from Time Machine.
Or, if it has to do with attempting a three-version leap in the OS. I'm not sure if this is related to other posts ( e.g.) I've seen about OWC SSD drives installed internally but appearing as external. The installer won't run on this drive, complaining that that it's missing a firmware partition. I am now trying to upgrade to High Sierra. Everything has worked fine up to now, although the OS still recognizes the SSD as an 'external' drive. Last year I replaced the Mac's internal 500GB SSD with a OWC Aura 1TB SSD. I have an early 2015 Macbook Pro running Mac OS Yosemite.
