returnDistinctValues does not always work

EdwardSohn2

Using:

var queryTask = new QueryTask(layer.layerObject.url + "?returnDistinctValues=true");

But sometimes this works and sometimes it does not.

Are there any server settings for each layer (featurelayer) that needs to be specified precisely to make the returnDistinctValues=true work?

Using v. 3.10.

EdwardSohn2

The layers apparently are both feature services and they both have supportsAdvancedQueries set to true.  But the returnDistinctValues=true are still not working...  (and yes the field is being sent as outFields parameter in the queries)...