In the jenkins-1.622 log4j was suddenly replaced by log4j-over-slf4j without any warning or even mention in the release notes.
log4j-over-slf4j jar has only partial implementation of log4j classes and interfaces. Many are absent or have an empty implementation.
That breaks plugins that use log4j.
I got the following errors:
It is possible to work around by using <pluginFirstClassLoader>true</pluginFirstClassLoader> , but that solution can potentially lead to classloading issues.