Several things that I noticed:
- Using 'ng-model' and 'k-ng-model' directives all together is not supported. If it has been working in the past, then that was only by chance.
- Since Q2 2015, the widget could not initialize if the provided model field is not defined (link
I would suggest you check the Troubleshooting section for AngularJS integration, as it explains how to deal with the changes in the implementation:
Telerik by Progress