image link in the database but images are not there at that linked folder

Hi,

I am facing a weird problem at my site (using listify theme). I have many listings and blog posts with images.

Randomly our images stop showing on the site. Just displays a ‘?’. In the backend, the url is present, size is not 0 however, there is no image corresponding to it in the folder.

I replaced these images with a fresh copy (from the backup). But recently this happened again and more than 100 images have become ?.

Any idea why this would be happening? I am using WP-Smush since the day the site was launched.

Thanks in advance,