Can this adapter be used to connect a thunderbolt 3 drive to a thunderbolt 2 port?

I have an Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter https://support.apple.com/en-us/HT207266

I have connected the thunderbolt 2 port on my mac mini (mid 2011) through this adapter to the thunderbolt 3 port on an external drive (Drobo 5D3). The volume mounts and I can read but not write to the external drive... write gives "error code -50". Also I cannot unmount the volume... diskutil unmountDisk /dev/disk3 gives "Unmount of disk3 failed: at least one volume could not be unmounted Unmount was dissented by PID 0".

Tried reboot of both mac and drive. Tried clearing the PRAM.

Ideas?