Time Machine backups are missing


I’ve searched the forums for this and haven’t found a fix for it. The links to info about Time Machine in similar threads no longer work.

Drobo FS, firmware 1.2.7

Macbook Air 7.2 OS 10.13.6, dashboard 3.4.2, Time Machine was set up in 2016.

iMac9,1 OS 10.11.6 (Bricked), dashboard 3.0.1 (can’t install 3.4.2 due to OS limitation), Time Machine was set up in 2011.

All backups are missing except yesterday and today. They were there within the last several weeks though.

I can see other files on the Drobo through Finder.

i can’t see Time Machine in the device menu in Finder.

Apple Care didn’t know enough about Drobo to help.

Drobo sent me here because my unit is old enough that it’s no longer covered by Drobo Care. I can buy support from them but they don’t cover data loss as a part of that service.

Any thoughts about next steps I can take myself?