Adobe Acrobat Pro Preflight tool Values

I am ghaving almost the same issue. (White line appearong on some proofs and not others at te bottom of the pages, adn all content mved up. Unfortunately, I created my book usinf Pages on a Mac, so added the required bleed to my page size. I had exchange of no less that 21 emails adn two live chats, with them telling me to add bleed. On the final "help chat", the aassistant acknowledged my book size page set up was correct. Amazon then told me to convert to PdfX, as it was the layers ot being flattened that was causing the trim issue. (I didn't think the layers had anything to do with the trim think so, but did it anyaway, as I now know Pdfx is a better conversion. Prior to that, I found out from another print firm that my Trim box was not showing. I am hoping that this will resolve my issue, but not sure. I have no idea what figures to enter i. nto the Trim and Bleed boxes, or even if this will fix the issue of teh white line, as it only appears at the bottom. Surely if there was an issue witht the trim, they would appear all round? Like you, I think my trim area is not centred (top / bottom) for some reason. At wits end! I must admit, Amazon have not been very helpful, adn seem to be giving conflicting info. Good luck with your project, and hopefully you'll eventually resolve it. Anyway, if anyon can tell me what I should enter in the 4 Trim boxes for a book (trim size 148x210mm)  and the bleed boxes, with Amazon bleed of 3.2mm on top / bottom and outer edge only (oddly, none required for the gutter) Thank you1