RHEL 7.6: Logins take 25 seconds to complete and messages such as "Failed to activate service 'org.freedesktop.systemd1': timed out" are seen in the journal

Issue

• Since updating to RHEL 7.6, users need 25 seconds to login and messages such as the one shown below are seen in the journal:

  [...] dbus[xxx]: [system] Failed to activate service 'org.freedesktop.systemd1': timed out
  [...] systemd-logind[xxx]: Failed to enable subscription: Failed to activate service 'org.freedesktop.systemd1': timed out
  [...] systemd-logind[xxx]: Failed to fully start up daemon: Connection timed out
  [...] systemd[1]: systemd-logind.service: main process exited, code=exited, status=1/FAILURE
  [...] systemd[1]: Failed to start Login Service.
  

• RHEL 7.6 periodically doesn't boot properly because polkit.service and tuned.service fail to start. This happens about 1 in 10 to 20 boots.