Tried switching to plain tty using Ctrl+(alt)+F[3-4].
Tried entering user credentials. They were rejected.
From there on, all my passwords prompts were rejected with “incorrect password” ( mostly for elevated privilages, but also logging out and logging in).
Until system restart.
Here in Canada, many users have configured support for both English and French. There are often problems with passwords with characters that use different keys depending on the “active” language.
Judging from the visible characters typed at the username prompt, both TTY and GDM are matched in the keyboard language, so that’s not an issue. Besides, one can also type in alternate accents with AltGr