Nextgen Images Not Indexing In Google

I’m using the Nextgen image browser and only the first image out of 30+ images has been indexed in google. I submitted a custom sitemap and once again only the first page where the first image is has been indexed. I’m not sure why this issue is there as when I tried with an image browser from a different gallery plugin I had no problem getting the images indexed in google.

https://www.ads-software.com/plugins/nextgen-gallery/