Hi, Try to add a delete step before the conversion, the delete step will unsure that previously converted line will be deleted.
you can also try the solution with CR described here, in this case because you have 2 KFs and one is not null the line will not be ignored. https://help.sap.com/saphelp_nw04/helpdata/en/09/078a63016311d393850000e8a597a0/frameset.htm
hope it helps.