In Kanboard 1.2.41, the function AuthController::logout was changed:
- fix: add CSRF check to the logout endpoint
See the details here.
As a consequence, each plugin that overrides the file Template/header/user_dropdown.php requires to be updated.
You could still continue using the latest Kanboard (recommended), if you
- update all your affected plugins, where available, or
- patch the all your affected plugins by hand, or
- apply my proposal below.