Jenkins slave cannot connect with master: Incorrect acknowledgement sequence

Question

After update of our Jenkins master installation to its latest LTS version 2.46.3 one of its slaves (Windows 7 machine, 32-bit) cannot connect with the master.

The er

Answer 1

We recently hit this issue with our AWS-based Jenkins using JNLP for remote integration testing. The remote slave would call back to the Jenkins master, which failed with a similar error. The issue ended up being a dynamically generated AWS ELB of type HTTP (because the Kubernetes ELB provisioner presently doesn't support multi-protocol ELBs) for the Jenkins Master. We had to manually change the JNLP ingress port type of the ELB to TCP, while the web interface ingress 'instance port' was protocol HTTP and 'load balancer' was protocol HTTPS.