Featured thumbnail images are not loading

Earlier it displayed featured thumbnail images of the posts in home page. But now it is not like that. Those features images are not displaying currently. But, when I click on ‘load more post’ button in home page and load previous posts it displays the featured images of those loaded posts.

After this issue occurred I am not able to set them as featured image in my newly written posts.

To check on this issue I have de-activate all the plug-ins that I have installed and checked. Also I changed my I had change the theme also to make sure whether it is a problem with my theme or not. But the problem didn’t get fixed.

Can anyone help me to sort out this issue.

My Blog: https://www.trickslanka.com