Error: Call to undefined method confSet() - prevents backup

Problem:
Backup and migrate worked fine on my local installation but failed on the remote server. Remote installation showed a very long PHP error, the problem being and undefined method: confSet() in the MetadataWriter.php file.

Troubleshooting:
My local installation did not show this error. I grepped Drupal core and vendor directories, and the backup_migrate directories, with no results for "confSet".

Workaround:
Commenting out the entire public function setUp function (starts at line 86) in MetadataWriter.php did not prevent the backup working in the local installation, and allowed the backup on the remote installation to proceed.