When using the search results webpart without the querystring (For instance when trying to use managed metadata navigation) I am unable to view custom managed properties AND am unable to see any hitsummary information.
For the example below, te webpart is configured with the query value directly inserted in it's query parameter under webpart properties. No other modifications were done.
In the following pictures, you can see the exact same query twice with the exact same result. Only without using the querystring the hitsummary information is missing. With the querystring my result is fine.