What exactly is not working on Wikidata as expected? Where is this jsondata query used? Is there an example page?

If I make a query (https://w.wiki/7to4), relying on P3896 statement in Q123002533 item, then for me this mapdata is retrieved using the following API link: https://commons.wikimedia.org/w/api.php?format=json&action=query&titles=Data%3ARoute%20through%20the%20landscape%20of%20cultural%20interest%20of%20V%C3%A9lez-Blanco.map&prop=revisions&rvprop=content&origin=*&maxage=3600

So by "fails" you mean that mapdata isn't diplayed on a map next to Commons link in this Wikidata item page? To me it seems that item pages just aren't set to display this data (using mapframe or otherwise). If I'm not missing something in browser console then it doesn't try to load respective jsondata on this page nor on any other item page with P3896 statement.

Just to explain the map gets rendered in Wikidata if using this gadget: https://www.wikidata.org/wiki/User:Teester/ClaimMaps.js

A working example is https://www.wikidata.org/wiki/Q122936541#P3896

Technically, User:Teester/ClaimMaps.js probably shouldn't be using jsondata to access the geojson, but action=query with prop mapdata. regardless, this does not explain why the endpoint was not returning the data, and why after purging it temporarily did before reverting back to missing it.

It now does seem cleared up. So perhaps it's a cache problem inside jsonconfig extension or something (which powers the Data namespace and the action=jsondata endpoint)

A working example is https://www.wikidata.org/wiki/Q122936541#P3896

Comparing the json data for this to that of original example I noted the latter for some reason had a capitalized "Name" property name (fixed here). Maybe this made it invalid?

Well, let's undone the change and wait for a day to see if the issue 'spontaneously' comes back and if not, then my other two changes. I guess then will give us our answer. Waiting a day is important, as that is the max cache time that is used in any of the chains.

Update: It was not the Name property. Gonna test now if it was the altitude or the other change

Update: It was not the Name property. Gonna test now if it was the altitude or the other change

Looks like it wasn't the altitude data either. And it probably wasn't the previous removal of properties either as we have another working example with exactly the same properties.

I now notice that the initial revision of this page was submitted with an empty data attribute. This is exactly what you received earlier, right? So most likely this bad revision was still cached at the time.