Delay of hours between blue and green on PostgreSQL RDS Blue/Green Deployment

We set up a blue/green deployment for our production PostgreSQL RDS during off-peak hours. However, shortly after the creation was completed, I noticed that the data in the Green environment was significantly behind the data in the Blue environment for a specific database, almost 2 hours behind when checking the record dates. This delay was increasing over time. We observed the WALDiskUsage metric gradually increasing, indicating that it was indeed accumulating WAL logs, but it wasn't anywhere near the limit we set (max_slot_wal_keep_size=100GB). The column "wal_status" in the "pg_replication_slots" table of this database indicated the value "extended," and the "wait_event" column in the "pg_stat_activity" table of the replication connection for this database indicated the value "WalSenderWriteData."

Does anyone know why this hours-long delay is happening? I found it very strange that the data is so many hours behind. I wanted to know if this is normal or if I need to adjust some logical replication parameter in PostgreSQL.

I appreciate any comments or suggestions on how to fix this.