I got my problem fixed. I tried ALL suggestions given to me by members (and thank you very much) and none of them worked: I used the DroboRepair (FSCK) operation, I unplugged each and every cable and connection and left it ‘cold’ for extended periods, I removed the drives and did a reset of the Drobo5n. I removed all drives from the 5n and put in a single, new, blank disk and did formatting and rebuilt the Drobo, and none of this worked to fix the problem: drives containing data were all in ‘good’ health, Drobo5n couldn’t mount, and health of Drobo read as ‘critical.’
But: I fixed it. What ended up working was - I found a mirror that still held Drobo firmware v.3.2.0. I installed that on the malfunctioning 5n appliance; restarted, and ignored the ‘warnings’ to upgrade to 3.2.3. So: I stepped back a version in firmware.
The thing came immediately back to life: Drobo Health = “good”, all drives and data intact, reading green, and I’m back in business now.
There should be a depot for older/legacy firmware and dashboard versions someplace. Someplace eas(ier) to get to. I think there may be something very wrong with 3.2.3. MHO…