Comment 1 for bug 1873892

seems undercloud wants to use "tripleo-admin" while it's unknown on the overcloud nodes:
Apr 22 00:52:15 overcloud-controller-0 sshd[9121]: input_userauth_request: invalid user tripleo-admin [preauth]
Apr 22 00:52:15 overcloud-controller-0 sshd[9121]: Connection closed by 192.168.24.1 port 39806 [preauth]

Fun fact, right after those failures, we have:
Apr 22 00:53:04 overcloud-controller-0 sshd[9124]: Accepted publickey for heat-admin from 192.168.24.1 port 41042 ssh2: RSA SHA256:fRwfBVrOBcn9OpHTu4Z1lhfJTfHtP0uw/12WLiTpmmM
Apr 22 00:53:04 overcloud-controller-0 sshd[9124]: pam_unix(sshd:session): session opened for user heat-admin by (uid=0)
Apr 22 00:53:04 overcloud-controller-0 sshd[9124]: pam_unix(sshd:session): session closed for user heat-admin

but on the undercloud, there's the timeout at 00:52 - guess the heat-admin connection is used by zuul|CI in order to get the logs and things.