Resolution:
In GridServer version 3.2 and earlier, a Command Service request may stop responding indefnitely if the underlying process fails.

Due to what appears to be a Java bug, even through the process no longer exists, all Java calls waiting on the process block forever as if it is still a valid process.

To correct this, set the Max Task Timeout on this Service, and set Kill Engine to "true" on the Service Rescheduler so that eventually the Engine is killed and the request is rescheduled.