Prioritize Visible Content

This issue is not directly addressed by the plugin but is likely to be addressed when you address the other issues, especially the ones addressed in the sections Eliminate Render-Blocking Javascript and CSS and Optimize and Resize Images so be sure to read those.

Essentially what this is saying is that too many resources have to be downloaded just to show the section of the page above the fold. Hence, the benefit of the above optimizations should become apparent. If these doesn't fix it or if you've resolved all the other issues and this is still left then unfortunately this is suggesting that a design change might be required to lessen the size or weight of the page, in particular the section that needs to be downloaded to render the page above the fold.