What does 'Missing in destination'/'Missed in destination' error mean?

If the "Missing in destination" message appears before a backup, it means that at the moment of the backup operation, files that are being backed up, don’t exist in the destination folder.

If the message appears after a backup, it means the file was not backed up. The most likely reason is that the file was used by another process and Handy Backup failed to gain read access to it.