I have not yet seen the eject before disconnecting error message unless either I pull the USB cable prior to ejecting the drive from Finder or unmount using Disk Utlity (and on the odd occasion on a reboot).
Usually on a reboot or restart the volume on the Gen 3 will mount just fine with full read/write capabilities. The issue I’m seeing will be Drobo Dashboard not seeing the Drobo and the capacity LEDs being too high. At this point I’ll eject the drive and then unplug/re-plug the USB and everything will be normal (volume mounts, DD sees the Drobo, capacity LEDs show correct number).
None of this happened with Catalina but because my Drobo still has capacity available and it seems I can safely read/write to the volume after restart/reboot I will stay on Big Sur. My other non-Drobo external USB drive works fine on Big Sur.
I’m hoping the issue is not a Drobo issue and might be resolved in 11.1 (currently in beta) because I’ve no faith Drobo/StorCentric will acknowledge this issue or resolve it (if it is actually their issue) in a timely fashion.
You describe a slightly different issue in that you are apparently seeing your drives as expected after reboot (do you mean Drobo Dashboard sees the drives normally, that Finder/Disk Utility does, or both?). In addition, you are seeing nightly improper eject error messages even though you have not rebooted your Mac. This last one seems odd to me. Have you checked what your uptime is in the AM? Maybe your system is rebooting overnight and reopening apps that were open when the system restarts. (you can tell what your time since last boot is by going to the Apple logo on the top left of the screen, clicking on “About This Mac”, then clicking “System Report…”, and then on “software”).
It still is very possible, and actually highly likely, that our issues are closely related but showing slightly different symptoms. Let’s keep our fingers crossed and hope for a speedy recognition of the issue and resolution.