When theme_blazy() does not understand a media output, it will print it as HTML as is. This HTML is normally a paragraph size. Check this to lazy load such HTML content (normally heavy third party contents, like oembed Instagram, Pinterest, etc.), no AJAX, otherwise printed as is. A new feature since 2.17, not battle-tested. Potential issues are with the attached libraries, and other various Blazy features. Please disable and report if any issues.