When you try to be perfect for your master-piece SEO-friendly wordpress website, you might have a lot of detail to craft and fix. In my site, I always see this messages whenever I create new content.
This message usually is triggered by the mix content of http and https. Here’s the a quick fix for you. Really simple.
1/ Check the page code source and find “http://”, if you can find any URL is under http://, it might be the root of the mix content problem.
2/ Goto Elementor > Tools > Replace URL
3/ Input your http address and https address accordlingly
4/ Save and done!
Then go back to browser and reload the page. You should see the site being secured again.