The Identify operation in ArcMap is unable to show attributes of a feature class in a map service with a join published to ArcGIS for Server 10.4 when the data source is from Microsoft SQL Server 2012.
Duplicate of BUG-000095875: This bug is fixed with the application of the ArcGIS for Server Publishing Patch (http://support.esri.com/download/7397) and a republishing of the affected map service.