Nelio Content integrates with Yoast SEO, one of the most popular plugins for WordPress. This plugin shows in the Yoast SEO box that appears when you edit a post some indicators about SEO and quality of the post you are editing.
When Nelio Content detects that you also have Yoast SEO installed, it includes these indicators within its own analysis.

In the Quality Analysis of Nelio Content Tools we may see that the content can be improved or that you should improve your Yoast SEO score. This means that we have to improve the quality of the input so that the Yoast SEO plugin gives us a positive evaluation.
You just need to inspect to the Yoast SEO’s box, see which aspects of the post should be improved, and make the proper changes to get a better evaluation. Find more details about Yoast evaluation here.