reported problem with Google indexing

[NedHenry]

Reported on Omeka forum:

"We have one exhibition that is not being indexed by Google, and can't understand why.

We're using the sitemap plugin, and have submitted the sitemap to Google via Google Search Console. But this one exhibition is still not being indexed (both before and after the sitemap was submitted). Can anyone suggest why?

Here's the exhibition: http://fusion.deakin.edu.au/exhibits/show/geelongad"

[NedHenry]

I can recreate the behavior, and am not sure why this happens. The URLs in the sitemap that are not indexed by google are valid and are formatted identically to the indexed URLs. As far as I can tell, I don't have any further control over how google indexes the sitemap after it is created and crawled. I would welcome advice from anyone who has insight into this.