Message "systemd[XXXXX]: Failed to connect to API bus: Connection refused" seen repeatedly in the journal

Issue

• The following messages can be seen repeatedly in the journal when a new user session is created

  [...] systemd[34548]: pam_unix(systemd-user:session): session opened for user XXX by (uid=0)
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Started Mark boot as successful after the user session has run 2 minutes.
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Reached target Timers.
  [...] systemd[34548]: Failed to connect to API bus: Connection refused
  [...] systemd[34548]: Starting D-Bus User Message Bus Socket.
  [...] systemd[34548]: Reached target Paths.
  [...] systemd[34548]: Listening on D-Bus User Message Bus Socket.
  [...] systemd[34548]: Reached target Sockets.
  [...] systemd[34548]: Reached target Basic System.
  [...] systemd[1]: Started User Manager for UID XXXUID.