RDFa markup not picked up in extractors

Hello,

I'm working on a project for the Dutch Kadaster and we're trying to improve findability of the datasets by adding Schema.org markup to the pages (as RDFa).
For example:

https://data.pdok.nl/datasets

The RDFa is valid, yet the data is not detected by, for example, the Google Structured Data Testing Tool:

https://search.google.com/structured-data/testing-tool#url=https%3A%2F%2Fdata.pdok.nl%2Fdatasets

If I put the same HTML on a different server, it works fine:

https://search.google.com/structured-data/testing-tool#url=https%3A%2F%2Fdemo.semaku.com%2Fpdok%2Fdatasets.html

So there is something about how the file is served from data.pdok.nl host that prevents extraction, but I can't for the life of me figure out what.

Is someone able to give me a pointer?

Regards,

John Walker
Principal Consultant & co-founder
Semaku B.V.
SFJ 4.009, Torenallee 20, 5617 BC Eindhoven
Mobile: +31 6 475 22030
Email: john.walker@semaku.com
Skype: jaw111
Web: http://semaku.com/

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