Mixed content

When i’ve successfully installed this plugin, everything runs fine. Until today, the image i added is no longer serve as https again. Google chrome tells me that ‘Attackers might be able to see the image you’re looking at on this site and trick you by modifying them’ and i found that those newly added image are getting warning while other older image not. Is there anything i done wrongly? plugins? theme? or i have to wait some times in order for the plugin to update?

currently installed plugins:
Akismet
Clef
CloudFlare Flexible SSL
Facebook Comments Plugin
Favicon by RealFaviconGenerator
Gmail SMTP
Jetpack
MailChimp for WordPress
Share Buttons by AddThis
Wordfence Security
Yoast SEO