Scenario: Create new App from scratch. Add a SharePoint list as the datasource. Add a Gallery Item and bind it to the datasource. The field that si defined as a Choice datatype is not shown as an available field.
Here is the list of fields in my SharePoint list.
This is what I see after adding the gallery and binding it to the datasource. notice that the 'Client Status' feild is not showing as an option to choose.
Let me know if you need any other details for this.