I think a quick thumbnail regeneration might cure this. Try using https://wordpress.org/plugins/regenerate-thumbnails/ or similar plugin, but backup your uploads dir before proceeding.

In order to just disable WP responsive images use this filter.

/**
 * Disable WP 4.4 srcset
 */
add_filter( 'wp_calculate_image_srcset', '__return_empty_array' );

I think a quick thumbnail regeneration might be the cure for this. Try using Regenerate Thumbnails or a similar plugin, but backup your uploads directory before proceeding.

In order to just disable WP responsive images use this filter.

/**
 * Disable WP 4.4 srcset
 */
add_filter( 'wp_calculate_image_srcset', '__return_empty_array' );