I have several dashboards build using JSON feed that I pulled using Tableau hosted WDC for JSON. I have not been able to refresh any WDC data source on all dashboards. I get similar errors across the board.
When using refresh extract, Tableau returns that fields are missing. You can't see it in this example but in most extract Tableau almost always returns fields as missing.
Then, when redirected to the data source panel, I get 4 new fields (query_count to query_results_body)
Work around was that I have to reload the API url on the WDC connector. When this method does not work I have to load a fresh extract and replace the old with the new.