Linearity and Heteroscedasticity Problems in Scatterplots

#1
I need to describe the pairwise relationships in this matrix scatterplot, and point out where there are issues with potential outliers, Linearity and Heteroscedasticity. This has been relatively straightforward for me to do, but I am stuck in describing the highly concentrated grouping of scores with right-angled appearance in some of the pairwise relationships. I have highlighted these on the image.

I think that the red highlighted scatterplots show a problem with heteroscedasticity, because the spread of scores on the y-axis is changing as you move along the x-axis.

And I think that the scatterplot highlighted with yellow may indicate an issue with linearity.

Is there a rule of thumb, that when you see "right-angled groupings" of scores in the corner of a scatterplot, it indicates a specific problem? Does this indicate a problem with linearity as well as heteroscedasticity? So for the scatterplots I have highlighted with red, do they actually show a problem for both L and H?

Kind Regards

Marked Scatterplot.jpg
 

Dason

Ambassador to the humans
#2
To me it indicates that one/both of the variables have an upper/lower limit that can be exceeded.