Drobo5D Thunderbolt and Big Sur

2019 MBP 16, i9: My Drobo5D won't mount after Big Sur update. Disk Utility sees it. Connecting it via USB and it mounts fine, although pathetically slow. Worked with RC2. Drobo Dashboard sees it. Both Disk Utility and Drobo Dashboard say it's healthy. Just backed up to a TM volume on this Drobo before the Big Sur Upgrade.

 Model Name: MacBook Pro

  Model Identifier: MacBookPro16,1

  Processor Name: 8-Core Intel Core i9

  Processor Speed: 2.4 GHz

  Number of Processors: 1

  Total Number of Cores: 8

  L2 Cache (per Core): 256 KB

  L3 Cache: 16 MB

  Hyper-Threading Technology: Enabled

  Memory: 32 GB

  System Firmware Version: 1554.50.3.0.0 (iBridge: 18.16.12561.0.0,0)