Slow to load additional items

Apologies if this issue has already been discussed or resolved, but I could not find anything with regards to the D8 version. Again not sure if it's just me or if it's a global issue.

Issue

I have a gallery view with about 100 photos and using the infinite scroll feature I'm able to gradually load all the photos. However the problem lies when loading the next lot of photos (12 per load).

The photos being loaded are medium size (240 x 240), using the default 'Medium' image style.

All medium image styles photos are being created and saved to the correct file path as normal.

When scrolling to see the next group of 12 photos, it is taking about 20 seconds to load and display. I could understand a delay like this if the system were regenerating the photos each time, but it's not, they already exist and are being used by the view output.

Is anyone else experiencing this, or something similar with a slower than expected load of the additional items?

Here is the page with the issue: http://www.ausgrainsconf.com/gallery/agic-australia-2017

Scroll and you should see the 20 second delay before the next lot of images show.

Thanks in advance.