After upgrading an old version of Sonarqube Scanner plugin (2.6.x) to the newest one, jenkins blocks on startup thread:

"CreationItemListener.onJenkinsStart" #42 daemon prio=5 os_prio=0 tid=0x00007fc028001000 nid=0x40 waiting for monitor entry [0x00007fc0d83ef000]
java.lang.Thread.State: BLOCKED (on object monitor)
at hudson.ExtensionList.ensureLoaded(ExtensionList.java:316)

• waiting to lock <0x00000006c82f45d0> (a hudson.ExtensionList$Lock)
  at hudson.ExtensionList.iterator(ExtensionList.java:172)
  at jenkins.security.ClassFilterImpl.isBlacklisted(ClassFilterImpl.java:303)
  at hudson.remoting.ClassFilter$1.isBlacklisted(ClassFilter.java:125)
  at hudson.util.XStream2$BlacklistedTypesConverter.canConvert(XStream2.java:563)
  at com.thoughtworks.xstream.core.DefaultConverterLookup.lookupConverterForType(DefaultConverterLookup.java:59)
• locked <0x00000006c7baa050> (a com.thoughtworks.xstream.core.DefaultConverterLookup)
  at com.thoughtworks.xstream.XStream$1.lookupConverterForType(XStream.java:498)
  at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:56)
  at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
  at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
  at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
  at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1189)
  at hudson.util.XStream2.unmarshal(XStream2.java:161)
  at hudson.util.XStream2.unmarshal(XStream2.java:132)
  at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1173)
  at com.thoughtworks.xstream.XStream.fromXML(XStream.java:1053)
  at hudson.XmlFile.read(XmlFile.java:147)
  at hudson.plugins.project_inheritance.projects.creation.ProjectCreationEngine.<init>(ProjectCreationEngine.java:380)
  at hudson.plugins.project_inheritance.projects.creation.ProjectCreationEngine.<clinit>(ProjectCreationEngine.java:317)
  at hudson.plugins.project_inheritance.projects.creation.CreationItemListener.onJenkinsStart(CreationItemListener.java:119)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:498)
  at hudson.init.TaskMethodFinder.invoke(TaskMethodFinder.java:104)
  at hudson.init.TaskMethodFinder$TaskImpl.run(TaskMethodFinder.java:175)
  at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:296)
  at jenkins.model.Jenkins$5.runTask(Jenkins.java:1095)
  at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:214)
  at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
  at java.lang.Thread.run(Thread.java:748)