Seeing negative values for logoff_lread intermittently in the dba_audit_session view

I've been working with our data warehouse team to do some analysis of session IO patterns for select users. We have had good results using the existing audit trail to track IO usage over time, but recently we have encountered an odd random event....it seems once in a while we'll get entries in the audit_session view that report NEGATIVE values for logoff_lread. It doesn't seem to be documented anywhere that I can find why we would ever see a negative value recorded (and in fact is odd to ever see this reported as negative from a logical design