@DarioV 

Hi, looking at the notes for this feature, it appears lock is expected.
 

During a MySQL backup operation of database that contains only innodb storage engine tables, when the MySQL dump command is executed with parameters master-data and single-transaction, an implicit lock is acquired on the database.

You can avoid the locking of database by using Percona XtraBackup utility to run MySQL backup operations. Using this utility, you can run non-blocking backup operation on the database that has tables of only innodb storage engine.

https://documentation.commvault.com/2023e/expert/93111_mysql_backup_using_percona_xtrabackup.html

So appears to be expected behaviour.

Regards,

Chris