You are using the Wordpress default gallery pages instead of our theme gallery page due to which it pixelated. Go to your Dashboard > Pages > all pages and edit your gallery page, Then remove code from page editor. Make it blank. Check image for reference. It will activate themes default gallery with slideshow. If not then follow process given below. Create a page choose gallery template media files upload files Cut that window without clicking insert into page button. It will resolve your issue.
