When an ArcGIS Dashboard element uses Categories from > Grouped values for data options, the source field menu is unable to be changed (it's grayed out) when referencing elements in the Dashboard driven by different data layers (for example, a different hosted table). However, the source field menu is able to be modified if the same data is used in an element which uses Categories from > Features.
The result of this situation is that when using the Grouped values setting, the ability of element A to influence the element B is very limited if the element B is driven by a different dataset than element A. This is the case even if the two data sets have a field in common (different than the field used to display data in element A) which could be used to drive the action of element B, since the source field menu can not be modified to allow the action to use compatible fields in the two different datasets.
The Grouped values option used to be more limited in the past regarding the types of map actions it could drive (like zoom, pan, and flash), but that limitation has since (happily) been removed. I'm hoping that a similar advance takes place for the ability to alter the source field when using this setting.
