Found this doc in Oracle support. May be it helps.
Oracle Support Document 1546358.1 (OBIEE 11g: Error:"OPMN.queryProcessStatus failed with the following exception" BIServer Component ( Coreapplication_obis1 ) does not Start after a Reboot and Status Shows as Stop). https://support.oracle.com/epmos/faces/DocumentDisplay?id=1546358.1
Hah good one! Hadn't thought of zombies.
Sometimes the most blindingly obvious answer is the right one and hence discounted because TOO obvious
I totally agree with you Christian.
Thank you for your support.