sjavac build failures: "Connection attempt failed: Connection refused"

During a recent Mach5 job, sjavac failed with the following:

jib > Compiling 100 properties into resource bundles for java.desktop
jib > [stderr] java.util.concurrent.ExecutionException: java.lang.NoClassDefFoundError: com/sun/tools/javac/util/Log$PrefixKind
jib > [stderr] at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
jib > [stderr] at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
jib > [stderr] at jdk.compiler.interim/com.sun.tools.sjavac.comp.PooledSjavac.compile(PooledSjavac.java:64)
jib > IOException caught during compilation: Connection reset
jib > CompileJavaModules.gmk:576: recipe for target '/cygdrive/t/workspace/build/windows-x64/jdk/modules/java.base/_the.java.base_batch' failed
jib > make[3]: *** [/cygdrive/t/workspace/build/windows-x64/jdk/modules/java.base/_the.java.base_batch] Error 1
jib > make/Main.gmk:202: recipe for target 'java.base-java' failed
jib > make[2]: *** [java.base-java] Error 1
jib > make[2]: *** Waiting for unfinished jobs....
jib > make[2]: INTERNAL: Exiting with 5 jobserver tokens available; should be 6!
jib >
jib > ERROR: Build failed for target 'default (product-bundles test-bundles)' in configuration 'windows-x64' (exit code 2)
jib > Stopping sjavac server