No job can be launched after Jenkins upgrade

After a Jenkins upgrade, jobs can no longer last more than a few seconds before ending with :

{{ ERROR: Aborted Maven execution for InterruptedIOException}}
{{ java.net.SocketTimeoutException: Accept timed out}}
{{ at java.net.PlainSocketImpl.socketAccept(Native Method)}}
{{ at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)}}
{{ at java.net.ServerSocket.implAccept(ServerSocket.java:545)}}
{{ at java.net.ServerSocket.accept(ServerSocket.java:513)}}
{{ at hudson.maven.AbstractMavenProcessFactory$SocketHandler$AcceptorImpl.accept(AbstractMavenProcessFactory.java:213)}}
{{ at hudson.maven.AbstractMavenProcessFactory.newProcess(AbstractMavenProcessFactory.java:282)}}
{{ at hudson.maven.ProcessCache.get(ProcessCache.java:236)}}
{{ at hudson.maven.MavenModuleSetBuild$MavenModuleSetBuildExecution.doRun(MavenModuleSetBuild.java:804)}}
{{ at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:496)}}
{{ at hudson.model.Run.execute(Run.java:1737)}}
{{ at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:543)}}
{{ at hudson.model.ResourceController.execute(ResourceController.java:97)}}
{{ at hudson.model.Executor.run(Executor.java:421)}}
{{ Finished: ABORTED}}

I've compared what is just before the exception in the previous working build, as you can see, some stable maven plugins packaged with Jenkins have been replaced with "alpha" jars which may or may not be the cause of the crash :

Working previous build :

[analyse-tweet] $ /var/lib/jenkins/install/jdk1.7.0_75//bin/java -cp /var/lib/jenkins/plugins/maven-plugin/WEB-INF/lib/maven31-agent-1.8.1.jar: /var/lib/jenkins/install/apache-maven-3.1.1/boot/plexus-classworlds-2.5.1.jar:/var/lib/jenkins/install/apache-maven-3.1.1/conf/logging jenkins.maven3.agent.Maven31Main /var/lib/jenkins/install/apache-maven-3.1.1/ /var/cache/jenkins/war/WEB-INF/lib/remoting-3.4.1.jar /var/lib/jenkins/plugins/maven-plugin/WEB-INF/lib/maven31-interceptor-1.8.1.jar /var/lib/jenkins/plugins/maven-plugin/WEB-INF/lib/maven3-interceptor-commons-1.8.1.jar 46935

Last non working build (with "alpha" plugins) :

[analyse-tweet] $ /var/lib/jenkins/install/jdk1.7.0_75//bin/java -cp /var/lib/jenkins/plugins/maven-plugin/WEB-INF/lib/maven31-agent-1.12-alpha-1.jar: /var/lib/jenkins/install/apache-maven-3.1.1/boot/plexus-classworlds-2.5.1.jar:/var/lib/jenkins/install/apache-maven-3.1.1/conf/logging jenkins.maven3.agent.Maven31Main /var/lib/jenkins/install/apache-maven-3.1.1/ /var/cache/jenkins/war/WEB-INF/lib/remoting-3.10.2.jar /var/lib/jenkins/plugins/maven-plugin/WEB-INF/lib/maven31-interceptor-1.12-alpha-1.jar /var/lib/jenkins/plugins/maven-plugin/WEB-INF/lib/maven3-interceptor-commons-1.12-alpha-1.jar 51312

Would there be a simple and safe way to downgrade jenkins or to solve this in any way ?