The keyword fragment fetch-url-http-3A-2F-2F... suggests a JavaScript fetch() call or a similar HTTP client incorrectly encoding the URL. In Node.js, Python, or browser environments (though metadata server is accessible from browsers), encoding can break the request.
http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/ The keyword fragment fetch-url-http-3A-2F-2F