Work Unit logs over written

I have a client that is experiencing process flow logs being overwritten with the 2nd part of the flow.
The start node information and all the actions up to a HRUA node are gone.
This occurs when an error from the HRUA signals the "not found" action.  The next node after the HRUA for "not found" is an email stating there is an issue with the flow.  The "not found" is occurring when a clear (unique) RMID is not found for the supervisor.
--
My first thought was that the log files were being deleted or archived.  The client is hosted by Velocity and they say this is not the case.
This only happens in PROD.  The TEST env is not experiencing this issue.
--
This is process flow integrator / "classic" process flow.  Not IPA.
--
Does anyone know of any settings that may cause this? 
Has anyone ever experienced this before?