Opening required backup file in Tools & Settings > Backup Manager results in error:
PHP Notice : Undefined property: backup_PmmRas_ResponseGetDumpDatabase::$_customHost
Plesk 12.5 with microupdate #22 is installed.
This is a software issue with internal ID PPPM-4121 . The fix will be included in further Plesk updates.
As the solution, replace
/usr/local/psa/admin/plib/backup/PmmRas/ResponseGetDumpDatabase.php file with attached one .