Scenario when running in the cloud: The browser console error you are mentioning above, should contain a reference to the widget.js file. If a linenumber is mentioned, check which widget encloses this linenumber.
Scenario when running the project locally: Set the 'bundle widgets' setting to 'true. This can be done by navigating in the Modeler to 'Project Module' > 'Settings' > 'Modeler' and tick the option 'Bundle widgets when running locally.
Once this is done, deploy your project locally. After deployment, navigate in your Mendix folder structure to the widget.js file located at: <your-project>-main\deployment\web\widgets\widgets.js and search for '_setValueAttr'. Once found, check in which widget this line occurs.
By this method you at least know which widget is causing this problem...