NaN% is the percentage representation of the fraction sitemap.xml/undefined.
The fraction sitemap.xml/undefined doesn’t have a numeric value because you can’t divide by something that isn’t defined. In mathematics this leads to an indeterminate result, which we express as NaN% when we try to turn it into a percentage.
Even though the number is not usable, it’s still helpful to talk about it. Saying the fraction equals NaN% lets people know the calculation can’t be completed in a normal way.
When you see sitemap.xml/undefined in a report, just remember it means the data is missing or incorrect, and the percentage will always show up as NaN%.
