GitHub Plugin settings not loaded on operations center startup after upgrading

Issue

After upgrading GitHub Plugin to 1.36, global GitHub settings are not loaded upon restart.

When you check under Manage Jenkins → Configure System → GitHub → GitHub Servers you will notice they are blank. You will also see the following stack trace during the startup of your operations center:

WARNING	hudson.model.Descriptor#load: Failed to load /tmp/joc-1-home/github-plugin-configuration.xml
com.thoughtworks.xstream.mapper.CannotResolveClassException: github-plugin-configuration
	...
Caused: java.io.IOException: Unable to read /tmp/joc-1-home/github-plugin-configuration.xml
	at hudson.XmlFile.unmarshal(XmlFile.java:199)
	at hudson.XmlFile.unmarshal(XmlFile.java:179)
	at hudson.model.Descriptor.load(Descriptor.java:933)
	at org.jenkinsci.plugins.github.config.GitHubPluginConfig.<init>(GitHubPluginConfig.java:86)
	at org.jenkinsci.plugins.github.config.GitHubPluginConfig$$FastClassByGuice$$1415135912.GUICE$TRAMPOLINE(<generated>)
	at org.jenkinsci.plugins.github.config.GitHubPluginConfig$$FastClassByGuice$$1415135912.apply(<generated>)
	...
	at jenkins.model.Jenkins.getRootUrl(Jenkins.java:2461)
	at com.cloudbees.opscenter.agent.OperationsCenterProtocolImpl.getInstanceIdentityCertificate(OperationsCenterProtocolImpl.java:516)
	at com.cloudbees.opscenter.server.model.OperationsCenter.configureAgentListener(OperationsCenter.java:1109)
	at com.cloudbees.opscenter.server.model.OperationsCenter.postInitialize(OperationsCenter.java:1121)
	at hudson.PluginManager$2$1$2.run(PluginManager.java:583)
    ...

Environment

Context

There have been other reports of similar symptomatic behavior of the GitHub plugin settings not loading on startup. In this case, the problematic plugin is the Operations Server plugin.

On controllers, other problematic plugins have been identified. See for example: - JENKINS-71786 (shiningpanda) - GitHub Plugin settings not loaded on startup after upgrading (support-core)

Workarounds

Any of the following can help workaround the problem:

After your controller restarts, go to Manage Jenkins → Configure System → GitHub → GitHub Servers and fill in the details again.
Use CasC for the operations center to set the GitHub plugin configuration.
Use a post init Groovy script to configure the GitHub plugin.

Tested product/plugin versions

CloudBees CI on traditional platforms - operations center 2.375.1.1 GitHub Plugin version 1.36