Dear @Anha
Could you take a screenshot of your backend- The Gridder?
What happens if you upload a new image into the Media Library and place it in the grid?
Is Lay Theme, Wordpress & Lay Theme's Addons all up to date?
Do you have any custom code that may interfere?
Do you have any Third-party Plugins that when temporarily de-activated, resolve the issue
https://laytheme.com/troubleshooting.html
Best wishes :)
Richard