OAuth cookie expiring, causing "Forbidden" errors upon saving files

Symptoms:

In the notebook: saving failed, showing a "Forbidden" error
In the logs:

[I 2021-09-21 09:28:50.206 SingleUserNotebookApp log:189] 200 GET /jupyter/user/xxx@yyy/api/contents/M1%20ISMH?type=directory&_=1632215401
727 (xxx@yyy@127.0.0.1) 2.69ms
[W 2021-09-21 10:26:16.081 SingleUserNotebookApp auth:314] No Hub user identified for request
[W 2021-09-21 10:26:16.082 SingleUserNotebookApp auth:552] Token stored in cookie may have expired
[W 2021-09-21 10:26:16.082 SingleUserNotebookApp zmqhandlers:275] Couldn't authenticate WebSocket connection

This may be related to the OAuth cookie improvement in JupyterHub 1.4. So upgrading from our current 1.3 to 1.4 as soon as it is released might fix the problem.

Potential mitigation: avoid long sessions? Explicitly doing a Control-Panel -> Stop my server, say during lunch breaks?

cc: @marcol480, @marchal