SEVERE: http://jenkins.example.com/ provided port:50000 is not reachable
java.io.IOException: http://jenkins.example.com/ provided port:50000 is not reachable
When we've found this (this occurred at night) we had changed JNLP port in Jenkins -> Configure Jenkins -> Confgure Global Security -> Agents -> TCP port for inbound agents -> Fixed from 50000 to 50001 and back to 50000 and then everything was working again (we use fixed port because we need to specify it in docker run settings when running Jenkins). It is reproducible on Jenkins 2.176.4.
How can I find the root cause of this? May be there are some debug options I can use or so... I've added logs listeners on classes I've seen in the logs and waiting when this will happen again.