Caching insecure content SSL problem

There is a caching problem for this home page. I’ve cleared the browser cache and the WP Fastest Cache and the problem still exists. The insecure content warning is referring to one of the slider images. But I’ve deleted that image from the server and all of it’s other image sizes and uploaded a new image file for the slider with a different name.

Yet it still hasn’t fixed the caching problem. The image file is nowhere on the server anymore after being deleted yesterday, but some caching still exists somehow. And the website is not on a CDN which could cause the problem.

Any suggestions?

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