Postgresql Replica is in sync but repmgr says node unattached
Maybe you can try running the following command from the standby node:

/usr/pgsql-10/bin/repmgr -f /var/lib/pgsql/repmgr/repmgr.conf standby follow


The paths of the repmgr file and the repmgr.conf configuration file may vary according to the installation.