Answer
Check the 'Line Item No' column in the source file — if it's set to 1 (indicating a package component line) instead of 0 (a plain, non-package part), the framework routes the record through package-component logic instead, which looks for PROBABILITY_TO_WIN in a different way and can't find a value even though your file has one at the record level. Setting Line Item No to 0 for non-package lines resolves this specific mandatory-field error.