During the checkout process an uncaught Exception is thrown that fails the build.

[DEBUG] IntegritySCM - Checkout on API thread: hudson.scm.APISession@fe9ee5
[INFO] IntegritySCM - java.util.concurrent.ExecutionException: java.lang.Exception:
MKS124803: Internal error detected: Exception was: java.lang.RuntimeException:
Release MKS Source registry for multiple updates: Attempt to release when not active!
[INFO] IntegritySCM - at java.util.concurrent.FutureTask$Sync.innerGet(null:-1)
[INFO] IntegritySCM - at java.util.concurrent.FutureTask.get(null:-1)
[INFO] IntegritySCM - at hudson.scm.IntegrityCheckoutTask.invoke(IntegrityCheckoutTask.java:361)
[INFO] IntegritySCM - at hudson.scm.IntegrityCheckoutTask.invoke(IntegrityCheckoutTask.java:25)
[INFO] IntegritySCM - at hudson.FilePath.act(FilePath.java:914)
[INFO] IntegritySCM - at hudson.FilePath.act(FilePath.java:887)
[INFO] IntegritySCM - at hudson.scm.IntegritySCM.checkout(IntegritySCM.java:789)
[INFO] IntegritySCM - at hudson.model.AbstractProject.checkout(AbstractProject.java:1411)
[INFO] IntegritySCM - at hudson.model.AbstractBuild$AbstractBuildExecution.defaultCheckout(AbstractBuild.java:651)
[INFO] IntegritySCM - at jenkins.scm.SCMCheckoutStrategy.checkout(SCMCheckoutStrategy.java:88)
[INFO] IntegritySCM - at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:560)
[INFO] IntegritySCM - at hudson.model.Run.execute(Run.java:1670)
[INFO] IntegritySCM - at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
[INFO] IntegritySCM - at hudson.model.ResourceController.execute(ResourceController.java:88)
[INFO] IntegritySCM - at hudson.model.Executor.run(Executor.java:231)

This happens only if the "Checkout Thread Pool Size" is > 1.

The occurrence of the exception is directly related to the "Checkout Thread Pool Size" : the bigger the pool, the more likely an exception is thrown.