postgres-01 and postgres-04 are not in the repmgr cluster

It seems that postgres-01 and postgres-04 are not part of the repmgr cluster:

$ sudo gitlab-ctl repmgr cluster show
Role      | Name                          | Upstream                      | Connection String
----------+-------------------------------|-------------------------------|-------------------------------------------------------------------------------------
* master  | postgres-02.db.prd.gitlab.com |                               | host=postgres-02.db.prd.gitlab.com port=5432 user=gitlab_repmgr dbname=gitlab_repmgr
  standby | postgres-03.db.prd.gitlab.com | postgres-02.db.prd.gitlab.com | host=postgres-03.db.prd.gitlab.com port=5432 user=gitlab_repmgr dbname=gitlab_repmgr

I tried adding postgres-04 using sudo gitlab-ctl repmgr standby register but this spits out:

Error running command: /opt/gitlab/embedded/bin/repmgr  -f /var/opt/gitlab/postgresql/repmgr.conf standby register
ERROR: INFO: connecting to standby database
ERROR: this node should be a standby (host=postgres-02.db.prd.gitlab.com port=5432 user=gitlab_repmgr dbname=gitlab_repmgr)

These two hosts should be added back to the cluster.