Time Machine started failing on an external USB drive.

> 
> Time Machine couldn’t complete the backup to “ExternalTimeMachine”.
> 
> 
> An error occurred while enabling ownership on the backup disk. You may
>  need to repair or erase the disk using Disk Utility. If the disk can’t
>  be repaired, select a different disk for backups.
> 
> 
> Latest successful backup: January 26, 2020
> 
> 
> 

I ran *First Aid* from *Disk Utility* and there are no problems.

I tried enabling ownership manually. The *Ignore ownership on this volume* option is missing for this Time Machine volume's *Get Info* in *Finder* whereas other volumes on the same physical drive have this option. I enabled ownership through the command line and Time Machine continues to have the same error.

```
$ sudo diskutil enableOwnership /dev/disk5
File system user/group ownership enabled
$ sudo diskutil enableOwnership disk5
File system user/group ownership enabled

```

*Disk Utility* reports the following:

```
Mac OS Extended (Journaled, Encrypted)
Type: CoreStorage Logical Volume
Owners: Enabled
Connection: USB
Device: disk5

```