Acronis True Image 2020 (Mac): Backup fails with "Failed to enumerate directory 'Macintosh HD — Data:/private/var/db/lockdown/" after update to macOS 10.15.4

Symptoms

After updating to macOS 10.15.4 backups fail with the following error:

The last backup as failed. Failed to enumerate directory 'Macintosh HD — Data:/private/var/db/lockdown/'. It may be corrupted or does not exist. Please check the disk for errors.

Cause

Catalina update 10.15.4 restricted access to folder /private/var/db/lockdown/ for security reasons.

Solution

As a workaround, exclude folder /private/var/db/lockdown/ from backup:

1. When configuring a backup, click Settings, and then click Exclusions;
2. Click the Plus sign, browse to the folder /private/var/db/lockdown/, select it and click Exclude.

More information

This issue will be fixed in future updates.