How are you trying to import content? Using an xml file exported from the old site? If so, is your old site still reachable on the internet? If you look at the contents of the xml file, you'll see that it includes links for the image files. So to import them, the old site must still be reachable. There are a number of reasons that this could happen. Another one is that the the import file contains custom post types and data related to a specific theme. If that's the case, make sure to switch your new Wordpress site's theme to match the old site's first.

Yes the site is accessible on internet, and I did check the image links in the exported xml file and they are too accessible

Nope I did try your suggestion but did not work, and I have an another droplet with one click install and it works perfectly there

The issue occurs only when I use Nginx, when I try with Apache import goes through smoothly