Why doesn't Let's Encrypt SSL certificate work on Iphone?

Question

iOS

Moved the site to another hosting. And I generated a free certificate from Let's Encrypt. Everything is great everywhere, except for the apple iphone and ipad. Writes "Failed to load", the error is not with me, but with the customer, so I can not check and understand what he does not like. If there is a sad experience - share, if there is this miracle of technology, check. I will be very grateful.
Website: https://volovik.org

Answer 1

style="background-image: url('http://volovik.org/images/blog/30/1492733619.jpeg'

Maybe because of this? There are 8 such fragments. On the page.

Answer 2

Because it's a partially secure connection. The page contains elements that are loaded using the normal http protocol. And this is found by simply visiting the page and viewing the properties of the connection.