After upgrading Jenkins from version 2.528.3 to 2.555.1, we are experiencing agent connectivity issues with the Jenkins controller. The error message displayed is: “This node is offline because it uses an old agent.jar.”
We attempted to resolve this by downloading the latest swarm.jar and also tested with different versions of the Swarm client JAR, but the issue persists. Both the Jenkins controller and agents have been upgraded to Java 21.
Please suggest a resolution.
