Hi,
Does this also happen on an actual device? If you use an older version of the widget tools, does it work then?
If your widget does not have native dependencies of its own, can you test it using the Make It Native app on a device?
If you can make it work using a previous version of the widget tools and it breaks after upgrading to the latest tools, this could be an issue with the widget tools. Submit a ticket to Mendix support in that case.
Be sure to eliminate any other issues as Mendix support does not debug your widget!