login failure: 20.04 / gdm3 / /usr/bin/Xwayland

[Jacques Beigbeder]

Hello Ubuntu users,

Environment: classroom (= many users)
  Ubuntu 20.04 up to date
  gdm3
  /usr/bin/Xwayland
  authentication: NIS
  HOME on an NFS server

Sometimes when an user logs, it fails.
And $HOME/.local/share/xorg/Xorg.* contains:
  [534963.743] (EE) systemd-logind: failed to get session: PID 1156040 does not belong to any known session
  [534963.745] (EE) xf86OpenConsole: Cannot open virtual console 5 (Permission denied)
  ...
  [534963.745] (EE) Server terminated with error (1). Closing log file.

When do this happen? Any fix?

NB: this is bad news when you try to defend free software...

Best regards,

--
Jacques Beigbeder                    |   Jacques.Beigbeder at ens.fr
Service de Prestations Informatiques |      http://www.spi.ens.fr
Ecole normale supérieure             | Tel : (+33 1)1 44 32 37 96
45 rue d'Ulm                         |
F75230 Paris cedex 05                |