You may run into this issue when executing the SharePoint 2013 Management Group SmartObject:
The property or field 'LoginName' has not been initialized. It has not been requested or the request has not been executed. It may need to be explicitly requested.
This issue will occur when you execute the following SmartObject Method: SharePoint 2013 > [Site Collection] > Management > Group > Is User In Any One Group
You may experience this issue after installing K2 5.1 FixPack 29.