Error code 13 for DB2 backup

Hello all, 

I got a question here. There is a DB2 backup that running as online backup. Previously, the backup will take up to 9 hour to finish. So what we did is, we add the @set db2_sessions=OPEN 2 SESSIONS WITH 4 BUFFERS BUFFER 1024 in the script (as like shown in the sample) to shorten the backup time. But what happen is confusing where the backup gave error code 13 for jobs but at the parent job the job status is 0. And it showing that the backup fiinsh in 2 hours and also able to list the DB2 backup image using command "bplist -C <client> -S <master_server> -t 18 -R/". 

So is it a successful backup or not. Is this some kind of bug?

Thank you