SiteGround's caching plugin:

https://wordpress.org/plugins/sg-cachepress/

... has a feature to lazy load images. If users have this installed along with Jetpack's lazy load feature, it can cause issues. Most of the time it's that images don't load properly.

I haven't investigated too deep, but I would think SG's solution integrates with their caching better than Jetpack's lazy loading, so we should consider disabling our feature when theirs is enabled.

When SG's lazy loading is enabled, siteground_optimizer_lazyload_images is set to 1 in wp_options. Maybe we can detect than and do this somewhere?

add_filter( 'lazyload_is_enabled', false );