Regarding Summary Plots and Missing Values in Principal Components Analysis

[#1]

I have some questions about the summary plot in principal components calculation.

The figure below shows the principal components results of the big class dataset for weight and height.

However, I don’t understand the mathematical meaning of the plot on the right. Weight point lies in the first quadrant—what does this imply? Also, what does the radius length represent?

Additionally, the figure below shows results for another dataset.

Under what circumstances can a summary plot be drawn, but when saving the principal components, both prin1 and prin2 are entirely missing values? What does this indicate? I cannot understand why prin1 describes 18.9% of the data and prin2 describes 13.6%, yet when saving the principal components, the data for them are completely empty.

[#2]

Multivariate Methods > Principal Components > Principal Components Report 

The Loadings Plot graphs the unrotated loading matrix between the variables and the components. The closer the value is to 1, the greater the effect of the component on the variable.

[#3]

Under what circumstances would summary plots be able to display the illustrations for component 1 and 2, but the 'save column' for 'save principal component value' is completely empty?

  

[#4]

For example when you have missing values