WordPress crops images differently on retina screens?

I am currently testing my websites on different types of screens and while my image cropping works perfectly on a non-retina screen, I am running into some cropping issues on retina screens.

I have two image sizes that are cropped to different dimensions. To achieve this, I have this in my functions.php file:

add_image_size('sidebar-thumbnail', 70, 70, true);
add_image_size('small-thumbnail', 300, 180, true);

On non-retina screens, the images crop perfectly for both sizes. However, on retina screens, the images look squished on one of the two sizes, for example:

retina small thumbnail
retina sidebar thumbnail

the sidebar-thumbnail is squished horizontally to fit in the square. In other examples, the sidebar-thumbnail looks fine but the small-thumbnail is stretched horizontally to fit the size. This is confusing to me because on standard-resolution screens both thumbnails are cropped perfectly, even when the same two images are displaying wrong on retina. Does anyone know what could be causing this?

Solutions Collecting From Web of "WordPress crops images differently on retina screens?"