Hi Antonia,
I'm not sure why these widgets got missing in your project (just verified, they are in the default project already available), but you can easily reimport them, in the Business Modeler press the 'App Store' button and search for 'AppCloudServices' and import it to your project. Then search for 'Feedback', and select and import the 'Mendix Feedback Widget' in your project.
That should solve the errors.