Cannot access external drive when IN Time Machine Backup
I back up my iMac (Late 2015) HD and an External HD with Time Machine using a Drobo 5N. I'm positive TM is backing up both drives because the size of the backup file (3.85TB) equals the used amount of space of the internal drive (500GB) plus the external drive (3.3TB).
However, when I enter TM, the External HD is greyed out. I cannot access/restore anything from it. Obviously, given its size, it's the more important of the two drives (70,000+ photos, tons of video), so I need to be sure that I can restore items from that drive.
How can TM be backing it up and yet not showing it when you enter TM???
I'm running Catalina 10.15.4. I suspect that my 2015 iMac and the latest software don't play together well as this has only been an issue since upgrading to Catalina (I THINK). But wouldn't it stand to reason that the TM backup wouldn't work at all???
See photo below. The "MyBook" drive is excluded from the backup.
iMac Pro