Some of the formatting may appear unpredictable because the PDF generator calculates how much space to allot for each element and then does its best to fill the space with content or information.
Product Information missing or cut off
The amount of space taken up by product information is exceeding the allotted space for that entire product. Shrink the font size or image size, or limit the number of attributes or products on the page.
General Spacing Issues
There is a lot of white space after a row of products. Or there are entire pages blank in between products.
The amount of space taken up by products is exceeding the allotted space for that row, causing the next row to be pushed farther down or off the page. Shrink the font size or image size, or limit the number of attributes or products on the page.
Blurbs have 2 modes of claiming space on the page: 1 line or Full Row.
If the blurb has 1-2 lines of text, it will only require a short banner's worth of space at the top of the page (around 1") and allow for the full number of designated rows of products to fill the rest of the page.
Blurb pushing products off page
If the blurb contents exceed 1-2 rows of text, the blurb will reserve a full row of products for itself instead. So if you chose 3 rows in your Page Layout selection, it may take up 1 row and only allow 2 rows of products to appear on the same page.
Text is getting cut off in a blurb
The text is either too much for the section or not using up enough space to expand its section. If the text is too long, cut a portion off and insert into another blurb. If the text is too short, add a few line breaks (hit Enter/Return) to see if it expands the section to claim a product row.