Dynamic Slider Not Working After 10 Posts

Hi,
I have Smart Slider running a dynamic slider showing post content (last 3 posts) on a page built with Elementor on a site running the Sydney theme and WordPress 4.9.9.
I’ve linked the site, it should look okay when you check because I’ve set the problem posts to ‘draft’ so the site will look okay while I work on the issue.
This worked beautifully until the 11th post was published when suddenly the featured image was not resized and instead showed full-size which screwed up the slider and the rest of the page. I tried changing images and had the same problem. I moved that post back to draft and the slider worked correctly as before. I moved some earlier posts to draft and republished the ’11th’ post and it worked fine. I’ve created new posts to test and anytime there are more than 10 posts it breaks. (Even though the slider is only showing the 3 most recent posts.)
The site is hosted on Bluehost and I have always felt that it is kind of slow (even when in the backend writing posts), not sure if this is relevent.
Any help is appreciated!
Thanks!

The page I need help with: [log in to see the link]