Mostly that problem is about the persmission for uploads folder of your wordpress website.
- So first, please check the permissions for your uploads folder. Start by navigating in your WordPress dashboard to Settings -> Media.
- Make sure that the option Organize my uploads into month- and year-based folders is checked.
- Next go into your Cpanel for your domain, whatever your hosting company provides for you to work with your website’s files or use FileZilla to reach your blog files. That is so much better than navigate by web browser.
- In your /wp-content folder, you should find your /uploads folder. Check the permissions assigned to this folder. If it’s anything other than 755 (or 777, though this might present a security risk), change the permissions.
- Go back to your Settings -> Media page in your WordPress dashboard, and then uncheck the Organize my uploads into month- and year-based folders option. Now check again to see if the thumbnails are loading.
