Post upgrade to 4.1.1 gallery images not showing

I’ve upgraded WordPress to 4.1 on a staging version of our site and I’m getting alt text instead of images on gallery pages e.g.:

I’ve tried the solution here : //www.ads-software.com/support/topic/galleries-stopped-working-1?replies=8

But this didn’t help. It seems that the src attribute for images is missing. There are no errors in the JS console.

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