Time Machine error code: 92

Catalina version 10.15.2 (19C57)

Mac (27-inch, Late 2013)

Using external drive as TM. Has been working on Catalina fine for several weeks. on January 15th started getting error message 92.

Ran First Aid - still got error

Unplugged and plugged drive in again - still got error

What is going on? I never had this issue with prior OS versions