Standby replication Lag
A read replica is a copy of the primary DB that reflects changes to the primary in almost real time, in normal circumstances. The lag represents the database server of the instance that is behind in seconds.
Technical Support will see alert incidents created for database replication lag for either the standby (far) database or read replica databases.
Note:
The cause will be DELETE or UPDATE statements. In the rare case, the cause is INSERT statements.