I'm using a 3rd party lib in my application that throws a java.util.EmptyStackException This only happens during the VM JIT/Warmup Start application Start stress test no rampup. java.util.EmptyStackException thrown Keep application and redo stress test. No exception thrown Shutdown application Start application Start stress test with rampup. No exception thrown I could keep reproducing this over and over. Anyone have any ideas on how I can trace this so I can give more info to the vendor? Or why it could even be happening? Thanks