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' );