Postgres repmgr - downstream nodes not attached
Some needed wal files to replicate wasn't found on primary.
Then I reinstated the standby cloning it again.

Commands submitted on standby server:

   pg_ctl stop
   repmgr -f /etc/repmgr/10/repmgr.conf --force --rsync-only  -h node1 -d repmgr -U repmgr --verbose standby clone
   pg_ctl start
   repmgr node status
   repmgr node check