We see seemingly random connection failures:

FATAL: CVS authentication failure while running rlog command
java.lang.RuntimeException: CVS authentication failure while running rlog command
at hudson.scm.AbstractCvs.getRemoteLogForModule(AbstractCvs.java:630)
at hudson.scm.AbstractCvs.calculateChangeLog(AbstractCvs.java:696)
at hudson.scm.AbstractCvs.postCheckout(AbstractCvs.java:715)
at hudson.scm.CVSSCM.checkout(CVSSCM.java:359)
at hudson.model.AbstractProject.checkout(AbstractProject.java:1367)
at hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild.java:674)
at jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:88)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:579)
at hudson.model.Run.execute(Run.java:1575)
at hudson.maven.MavenModuleSetBuild.run(MavenModuleSetBuild.java:477)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:237)
Caused by: org.netbeans.lib.cvsclient.connection.AuthenticationException: SSH connection failed.
at org.netbeans.lib.cvsclient.connection.SSHConnection.open(SSHConnection.java:141)
at org.netbeans.lib.cvsclient.Client$1.run(Client.java:374)
at java.lang.Thread.run(Thread.java:722)
Caused by: com.jcraft.jsch.JSchException: verify: false
at com.jcraft.jsch.Session.connect(Session.java:307)
at com.jcraft.jsch.Session.connect(Session.java:160)
at org.netbeans.lib.cvsclient.connection.SSHConnection.open(SSHConnection.java:139)
... 2 more

There is a (fixed in 1.50) jsch bug, which seems related. I updated our Jsch yesterday and since then no more connection errors occurred (Before it occurred at least a few times a day, so I'm pretty confident that 1.50 fixed the issue).