> But why is "source not found" the expected behavoir? shouldn't there be a valid class loaded?
"source not found" means that it is provided by the JVM jar(s) directly and this is what we desire. Sometimes, it's an old/outdated XML parsing implementation that it loaded and you get a source such as ".../xercesImpl-2.6.2.jar". It is often caused by plugins forgetting to exclude old versions of Xerces from their dependencies.
> openjdk version "1.8.0_212"
This is a JDK that works well. The problem is likely to be a plugin that pull an outdated version of XercesImpl
class org.apache.xerces.jaxp.DocumentBuilderFactoryImpl -> file:/var/jenkins_home/plugins/registry_reporter/WEB-INF/lib/xercesImpl-2.6.2.jar