I've created a new master page and page layout in Design Manager. When I preview the page layout in Design Manager, the layout appears correctly with no errors (see below).
The new layout also appears in the Page Layout options
However, when I apply the new page layout to a page, it seems that the stylesheet is not linked as it kicks out the text without the hero unit, text styles, columns, etc.
I've checked in SP designer that the CSS file is checked in and published and the .css link shows up in the HTML page layout file.