I don’t see the ‘read more’ button on any of the currently displayed homepage posts which usually indicates that the posts have manual excerpts.
Your site is accessible both via HTTPS and plain HTTP, however WordPress is configured to use the secure URL. When trying to use the ‘more posts’ functionality when the site is accessed via plain HTTP, the additional posts fail to load because the browser rejects mixing HTTP and HTTPS content. To resolve this you should make your site only accessible via HTTPS.
When I access the site via HTTPS, I can see the issue you are reporting. I also notice that the images should be loaded from the ix.w.org URLs which means you are using Jetpack’s image optimization functionality.
The images returned from those URLs are 1×1 pixels in size. I couldn’t tell you why this happens, but turning off the image optimization should alleviate the problem.