The issue started occurring after the upgrade.
This issue is only applicable to ADM devices in HA on 12.1 and 13.0 versions.
Starting from ADM on-prem 13.0 71.x release, if database streaming between the nodes in an HA deployment fails, now you can click the Sync Database tab under System > Deployment > High Availability Deployment in the ADM GUI, to restore the database.
Alternatively if you are on version less than 13.0 71.x, then use the following procedure:
# cd /var/mps/db_pgsql/data/pg_log
# chown mpspostgres *
# nohup sh /mps/scripts/pgsql/join_streaming_replication.sh SecondaryIP PrimaryIP nsroot > /var/mps/log/join_streaming_replication_console.log 2>&1 &
# nohup sh /mps/scripts/pgsql/join_streaming_replication.sh SecondaryIP PrimaryIP > /var/mps/log/join_streaming_replication_console.log 2>&1 &
# tail -f /var/mps/log/join_streaming_replication_console.log
# ps -ax | grep -i wal
?? Ss 0:14.14 postgres: wal receiver process streaming