The elastic axis plugin allows a multiconfiguration job to use an axis label that expands to match all agents with that label. That is quite helpful when I want to run an administrative task on all linux agents or all windows agents.

With Jenkins 2.249.1, the label verification code has been significantly improved. One of those improvements removed a message that is referenced by the elastic axis plugin. Because the message is no longer available, the elastic axis plugin configuration UI writes the word "ERROR" instead of telling the user what is wrong with the comma-separated list of labels they provided.

The incorrect UI looks like this:

The error message is disconcerting, but does not prevent the user from saving the form and does not prevent the job from running. The failure is only in form validation.