It depends on your priorities. If you’re keen to keep your existing backups there are probably ways of repairing them. If you just want to get your computer backing up again then trash the relevant share and start again. As a compromise, if you have the space, you could abandon the existing Time Machine share with a view to trying to fix it later and create a new share for immediate use.
Thanks for your assistance. The same issue started with my MacBook Pro so I decided just to reset the Drobo 5N and reestablish the shares. When that was completed the backup of the Mac Pro started fine.
As a matter of curiosity can you trash just one share and redefine it to start again without resetting the entire 5N? How?