Since updating to version 2.9 of the lockable Resources plugin we get the following error when trying to lock a resource through the /lockable-resources/ GUI.

HTTP ERROR 403 No valid crumb was included in the request

Switching back to version 2.8 and restarting Jenkins fixed that issue.

This is an critical issue and we are forced to stay on version 2.8 for now, even if that version has open CSRF vulnerabilities.

Jenkins Version: 2.249.1 (LTS)

I also opened this issue on GitHub (https://github.com/jenkinsci/lockable-resources-plugin/issues/216) but I think the Jenkins bug tracker is a more appropriate place for it!?