If you use a proxy server for your local SAPUI5 development, then do not forget to adjust the rootURI of the mock server configuration as well. The rootURI of the mock server configuration must be exact the same as the data source uri of the manifest.json.
![SAPUI5 App: Running mockServer.html](https://i0.wp.com/blog.surges.eu/wp-content/uploads/2021/03/cors_mock_server_rooturi.png?resize=525%2C346&ssl=1)