If they weren’t to boot drives, then they may just need to be remounted. Check with Disk Utility.
They are boot drives and scratch drives. I have them all up and working again by downgrading. High Sierra insisted on formatting all the SSDs in the new format, caused some drives to fail to appear, not worth the trouble as the land lies currently. Will just have to wait until it matures.
I am running some of the SSDs from PCI and some as SATA and a couple USB3 all gave same problem.
I think the mixed format on the drives caused some of the problem but I am satisfied that I don't currently need the new features bad enough to worry with it. I guess I can blame Crucial but I doubt they are the total problem.
Getting too old to keep up Sword but still young enough for the challenge. have a G4 Mini running Tiger and Classic when I get he urge to dwell in the past.