Solid Backups Multisite functionality is EXPERIMENTAL and NOT officially supported.
Multiple issues are known. Usage of it is at your own risk and should not be relied upon. Standalone WordPress sites are suggested. You may use the “Export” feature to export your subsites into standalone WordPress sites. Not all Standalone features are available for Multisite installations. Please carefully review the features, differences and limitations so that you are aware of them and are sure it will meet your needs.
You must add the following line to your wp-config.php to activate these experimental features:
define( 'PB_BACKUPBUDDY_MULTISITE_EXPERIMENT' , true );