feature image size issue

everything was working good with my blog until a month or so back. then i noticed that my feature images were automatically being resized to a rectangle vs a square. my older posts still have the square image. but all my new ones are resized. I thought it was the theme, and reached out to them, but we realized the change is seen from the wordpress side. when im writing up my post, I can now see that in the sidebar where you can add your feature image, the preview image has changed from the square to the rectangle. how do i change this back? ive looked at my images and they are set to square dimensions.

The page I need help with: [log in to see the link]