PO Approval Workflow fails with message “Concurrent program returned no reason for failure”.

Hello

We have a scheduled Workflow Background Process that runs every hour for PO Approval with Deferred=Yes and Timeout=No. It has been failing since Jan 23 at 2:15 PM with the message “Concurrent program returned no reason for failure”. Examining the ICM log finds the entry (like):
Found running request 12969920 attached to dead manager process.
Setting request status to completed.
Found dead process: spid=(7396), cpid=(900120), ORA pid=(402), manager=(0/0)
We have other Workflow Background Process requests running for different item types at different schedules throughout the day and none of those complete in error. We have run it under different id's (including SYSADMIN) with the same result.