Change in (post_thumbnails_divi.php) file:
'400x9999' => 'et-pb-post-main-image',
vs
'400x250' => 'et-pb-post-main-image',
Change in (post_thumbnails_divi.php) file:
'400x9999' => 'et-pb-post-main-image',
vs
'400x250' => 'et-pb-post-main-image',