TLJH not working after upgrading from Ubuntu 18.04 to 22.04

[vsisl]

Bug description

After upgrading from Ubuntu 18.04 to 22.04, my TLJH installation stopped working.

When going to http://localhost:80, I get "Bad Gateway".

Systemctl says that jupyterhub.service failed to start.

$ sudo systemctl status jupyterhub.service
× jupyterhub.service
     Loaded: loaded (/etc/systemd/system/jupyterhub.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Tue 2023-12-12 11:59:16 CET; 12min ago
    Process: 6346 ExecStart=/opt/tljh/hub/bin/python3 -m jupyterhub.app -f /opt/tljh/hub/lib/python3.6/site-packages/tljh/jupyterhub_config.py --upgrade-db (code=exited, status=1/FAILURE)
   Main PID: 6346 (code=exited, status=1/FAILURE)
        CPU: 74ms

Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Scheduled restart job, restart counter is at 5.
Dez 12 11:59:16 Persephone systemd[1]: Stopped jupyterhub.service.
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Start request repeated too quickly.
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Failed with result 'exit-code'.
Dez 12 11:59:16 Persephone systemd[1]: Failed to start jupyterhub.service.

tljh-config reload hub throws an error.

$ sudo tljh-config reload hub
Traceback (most recent call last):
  File "/usr/bin/tljh-config", line 6, in <module>
    from pkg_resources import load_entry_point
ModuleNotFoundError: No module named 'pkg_resources'

Edit: Here's output of journalctl -u jupyterhub

$ journalctl -u jupyterhub
Dez 12 11:59:16 Persephone systemd[1]: Started jupyterhub.service.
Dez 12 11:59:16 Persephone python3[6346]: /opt/tljh/hub/bin/python3: Error while finding module specification for 'jupyterhub.app' (ModuleNotFoundError: No module named 'jupyterhub')
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Main process exited, code=exited, status=1/FAILURE
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Failed with result 'exit-code'.
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Scheduled restart job, restart counter is at 5.
Dez 12 11:59:16 Persephone systemd[1]: Stopped jupyterhub.service.
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Start request repeated too quickly.
Dez 12 11:59:16 Persephone systemd[1]: jupyterhub.service: Failed with result 'exit-code'.
Dez 12 11:59:16 Persephone systemd[1]: Failed to start jupyterhub.service.

How to reproduce

1. Installed TLJH on Ubuntu 18.04 following documentation. (This was done a few years ago already.) In particular, I used Xubuntu 18.04.
2. Upgraded to Xubuntu 22.04 using desktop environment.
3. TLJH not working anymore.

Any help would be highly appreciated! Please let me know if I should supply additional information.

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