How were the fields created and where does the data come from? Is this a feature class from AGOL or ArcGIS Server? If you bring in the data as an external data source and hook up the list widget, can you reproduce?
I created the fields in AGOL after building the dashboard application.
The only way I found to fix the problem was to override the feature class in AGOL with a downloaded copy of the feature class using ArcMap 10.3.1