If you are using https and you still get this message, It’s because you imported demo from http://wilcity.wiloke.com/
When using https, it requires 100% link must be appended https instead http.
EG: Your website is website.com, and you are using http. If your content inserted an image like this http://website.com/image.png, and you want to migrate your site to https://website.com, You will have to re-update it to https://website.com/image.png after that.
Because of importing data from http://wilcity.wiloke.com/, some images are using http still, to resolve this image, You will need to replace all imported images with yours. Which means you will have to replace Icon Image and Featured Image of Listing Location, Listing Category, Listing Tag, and Listing Content Image with yours.
To replace Listing Category, Listing Location, Listing Tag, please click on Listings -> Listing Categories/Tags/Location/ -> Select 1 Category / Tag / Location -> Re-upload Icon Image, Featured Image with your.
To replace Listing Content Image, simply delete Listings under Listing or replace Listing Content with yours.