Alright. Firing up the #ETL Mapper. It's called "#Mapper", a product by #GXS, now owned by #OpenText. These organisations manage huge UPC catalogs used by thousands of trading partners for selling and buying products.
The problem: there is a disconnect between the data rows coming in, and the output. No incoming rows get put out. So I'm checking the map for hidden criteria and evaluations. And retesting after each change.