An other testcase which may be shot in the same direction:
About a promotion->parameterized-trigger->downstream-ext I start manually a jenkins-job as a subtasks. This hang at the point "[EnvInject] - Injecting contributions.". If I cancel this subtask, I have got following error message:

Run condition [Always] enabling perform for step [Shell ausführen]
11:04:48 ERROR: Publisher org.jenkins_ci.plugins.flexible_publish.FlexiblePublisher aborted due to exception
11:04:48 java.lang.NullPointerException: no workspace from node hudson.model.Hudson@3d03a85f which is computer hudson.model.Hudson$MasterComputer@29c6774 and has channel hudson.remoting.LocalChannel@25e48494
11:04:48 at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:76)
11:04:48 at hudson.tasks.CommandInterpreter.perform(CommandInterpreter.java:66)
11:04:48 at org.jenkins_ci.plugins.run_condition.BuildStepRunner$2.run(BuildStepRunner.java:110)
11:04:48 at org.jenkins_ci.plugins.run_condition.BuildStepRunner$Fail.conditionalRun(BuildStepRunner.java:154)
11:04:48 at org.jenkins_ci.plugins.run_condition.BuildStepRunner.perform(BuildStepRunner.java:105)
11:04:48 at org.jenkins_ci.plugins.flexible_publish.ConditionalPublisher.perform(ConditionalPublisher.java:134)
11:04:48 at org.jenkins_ci.plugins.flexible_publish.FlexiblePublisher.perform(FlexiblePublisher.java:111)
11:04:48 at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
11:04:48 at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:804)
11:04:48 at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:776)
11:04:48 at hudson.model.Build$BuildExecution.post2(Build.java:183)
11:04:48 at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:725)
11:04:48 at hudson.model.Run.execute(Run.java:1701)
11:04:48 at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
11:04:48 at hudson.model.ResourceController.execute(ResourceController.java:88)
11:04:48 at hudson.model.Executor.run(Executor.java:231)

An other fact is, jenkins create the workspace in the path "/root/jenkins/". In the post build process, I write now the environment variables to a file. Here are the most importants:

HUDSON_HOME=/intranet/jenkins
JENKINS_HOME=/intranet/jenkins
HOME=/root
PWD=/root/jenkins
WORKSPACE=jenkins

Which version are you updating from? Does it happen with projects not using EnvInject, or on instances where EnvInject is not installed? Did you upgrade any plugins around the same time this broke?

We used the Jenkins ver. 1.525.

The information about a installed plugin "EnvInject" are strange, because in the file path exist the version "1.89". The jenkins-plugin-manager said, that it is not installed and it is not listed for an installation or an update.

We updated our jenkins last week to the version 1.596. Now it works.