I ran this down, @cculber2. It appears that the first/last line-items can be clipped during the CSV import process if the browser OS does not match the Tiller Money Labs add-on’s “script timezone” (PST).
In the case where all line items fall on a single day (like your Amazon returns example), a browser in the EST timezone can filter out all results.
It’s a bit of a hack but I just published a change to expand the filter start and end date windows by 6 hours. This should address the issue for US-based users at least.