Need help with add_image_size()

Greetings,

I created a function to add custom image sizes to the image editor window. The names of the new image sizes have been added but the image dimensions inside the add_image_size() function have been ignored. I have no idea where the sizes in the image editor window came from.

Here is the code:

if ( function_exists( 'add_image_size' ) ) {
		add_image_size( 'featured-image-500', 500, 250 );
		add_image_size( 'x-large-thumbnail', 200, 200 );
		add_image_size( 'medium-plus', 390, 390 );

	} 
	function extra_image_sizes( $sizes ) {
  		return array_merge( $sizes, array(
    	'featured-image-500' => __( 'Featured Image 500px' ),
    	'x-large-thumbnail' => __( 'X-tra Large Thumbnail' ),
    	'medium-plus' => __( 'Medium Plus' ),
  ) );
}
add_filter( 'image_size_names_choose', 'extra_image_sizes' );

Here is what I am seeing in the image editor window.

What am I missing?

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