I think I might have hit this finally. The blank purple screen with a mouse cursor probably means the shell failed to start. And indeed I have no gnome-shell process running for my UID. The journalctl shows:
pr 23 14:33:47 haz gnome-shell[912]: g_dbus_connection_call_sync_internal: assertion 'G_IS_DBUS_CONNECTION (connection)' failed -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gdm3 in Ubuntu. https://bugs.launchpad.net/bugs/1766137 Title: Login fails when preceded by incorrect password To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1766137/+subscriptions -- desktop-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
