Where did new database 'BackupLocDb_###" come from?
The database is created when you use the GUI to add databases to the secondary servers, and select the option Full database and log backup, you may safely delete it.


  In the Specify a shared network location accessible by all replicas: field, specify a backup share to which all of the server instance that host replicas have read-write access. For more information, see Prerequisites, earlier in this topic. In the validation step, the wizard will perform a test to make sure the provided network location is valid, the test will create a database on the primary replica named "BackupLocDb_" followed by a Guid and perform backup to the provided network location, then restore it on the secondary replicas. It is safe to delete this database along with its backup history and backup file in case the wizard failed to delete them. Source