More discussions about the futility of this error: https://developer.apple.com/forums/thread/655840?page=1#738339022

Same problem on TWO mac minis I just bought (Intels were on sale). Both have fusion drives. errors on the Container disk only. Safe boot - same. Recovery Disk Utility - same. Reinstalled Mojave on both - same errors. DiskDX says both fusion drives are fine. Maybe it is Mirosoft Office items - I've read of problems with OneDrive and the notes that come with it (I don't use them but they were installed). Uninstalling them didn't help, however. No solutions on the web so far.

I've come to believe this was caused when I created a boot disc from a Carbon Copy Cloner clone instead of Time Machine. Just a theory, but for me it seemed to be the cause.