This may be related to the issues seen by users to configure the
account. This bug is only confirmed on Firefox on Mac.

The configuration error is a 500 due to a missing 'password' field in
the session, probably related to a clear of the session.

This clear of session only being done on the opening of the /config
page, it could be that Firefox reload the page or re-do a query in the
background, hence clearing the session.

This bug is not reproducible on Chromium nor Firefox on Linux.