5D not seen by Dashboard

I’ve had my 5D since 2014. I have been using connected to the thunderbolt port (using a thuderbolt 3 to 2 adapter) no problem until recently. A few months ago it stopped mounting sporadically. Rebooting the 5D would sometimes bring it back. 2 days ago I tried swapping cables and it was working for awhile. Last night it stopped again so I tried a new adapter and it started getting recognized again. This miorning not seen again. I uninstalled Dashboard and reinstalled it. Still wouldn’t see the 5D. For the hell of it I switched from thunderbolt to usb. The drives now mount via the Mac OS, but are still not seen by the dashboard app. Any idea how to get this working again?
Oh and one more anomally. Last year after a drive failed I upgraded from the original 4gb drives to 8gb drives. For some reason dashboard created a second parttion, but both partitions were seen as being the same size. Last week I backed up both to a 16gb external drive, and reformatted the Drobo. However the newly reformatted drive shows as being 70gb, and not the actual 16gb (using dual redundancy).
Late 2020 iMac
Big Sur 11.4

You’ll need to wait for a Mac user to help troubleshoot Drobo discovery on a Mac. I’m in a Windows environment.

However, the behaviour when expanding disk sizes is expected & normal. Older firmware only supported 16TB volumes & created a new one every time storage was available to do so, newer supports 64, but it takes a reset/reformat to enable the support, without the reset/reformat the unit carries on working as per the old firmware. Having reset it, you’ll now see one huge volume rather than 16TB chunks.

Will resetting lose my data?

Yes if you do it with the drives installed, but from your description there’s no longer any need since you apparently did it already as part of that backup & restore routine.

If you wanted to do a reset & preserve your data you could do one with the drive pack removed, then power off & put the drives back in… There’s a small chance that a reset might sort the discovery issues out, though my feeling is that’s more likely to be something funky about MacOS rather than the actual Drobo.

I’ve been holding off on installing Monterrey but maybe I’ll try updating to Big Sur 11.6.1

I updated the OS and went back to a thunderbolt connection. Dashboard is now seeing the drive. Probably just a reinstall of the original OS would have fixed whatever got screwed up. Hopefully all is recognized the next time I reboot. If so I will go through the reset to get the drive sizeing corrected

Just tried a reset with the drives removed and it still sees 70tb and not 18. I may have to do a reset and reformat and restore to get that right

With the new (current) firmware a reset is going to provision a volume of 64TiB (binary) I’d expect that to show as about 70TB (decimal).
This is normal, expected, and correct.
Offhand I don’t know a way to force it to use the old volume sizes short of downgrading to older firmware, something I don’t recommend except if you’re told explicitly you need to by Drobo support to deal with some problem.

So that would be classified as a bug if I actually have only 30gb of binary storage before allowing for redundancy

It’s thin-provisioning, it creates a volume the OS using it sees as a given size (64TiB), while doing the redundancy/data protection invisibly & alerting you (via dashboard or lights) when it needs bigger drives to actually store your data & protect it. Gives you the ability to upgrade drives without having to reset/reformat or backup/restore or manage multiple smaller volumes.

It’s exactly the original behaviour, just with an initial thin-provisioned volume 4 times the size.