https://github.com/jenkinsci/envinject-plugin/blob/f72ef372efdef8791a175f1c121e067c10da40a6/src/main/java/org/jenkinsci/plugins/envinject/service/EnvInjectMasterEnvVarsSetter.java#L35 uses Field.class.getDeclaredField("modifiers") to remove the "final" modifier from the static field EnvVars.masterEnvVars (https://github.com/jenkinsci/jenkins/blob/f23512f2bc97d18cd4f0183a7db4a62bc6b84196/core/src/main/java/hudson/EnvVars.java#L459). This method is no longer working on OpenJDK 12+.

According to https://bugs.openjdk.java.net/browse/JDK-8217225?focusedCommentId=14237541&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14237541:

The change in JDK 12 is intentional to improve the robustness and security of the platform. In general, there is no supported way to change static final fields.

This error can be seen in the logs as:

onOnline: class org.jenkinsci.plugins.envinject.EnvInjectComputerListener reported an exception: java.io.IOException: org.jenkinsci.lib.envinject.EnvInjectException: java.lang.NoSuchFieldException: modifiers