onProxyRes of http-proxy-middleware doesn't work for same cases

Question

I'm trying to write a proxy using http-proxy-middleware that modifies the content of the response, and set some headers.
I'm intercepting the reponse using responseInterceptor as the documentation says.

Here is the proxy implementation

const proxy = createProxyMiddleware({
    target: "http://www.google.com" ,

    changeOrigin: true,
    /**
     * IMPORTANT: avoid res.end being called automatically
     **/
    selfHandleResponse: true, // res.end() will be called internally by responseInterceptor()

    /**
     * Intercept response and replace 'Hello' with 'Goodbye'
     **/
    onProxyRes: responseInterceptor(async (responseBuffer, proxyRes, req, res) => {
        res.setHeader("custom-header", "header-value");
        const response = responseBuffer.toString('utf8'); // convert buffer to string
        return response.replaceAll('Hello', 'GoodBye'); // manipulate response and return the result
    }),
});

The issue is related with the target, for example for the target google.com it works perfectly, but using notion.so I'm getting an empty response buffer (so I can't modify it, neither the headers), but finnaly the proxy returns the response without any changes. Is onProxyRes calling before receiving the response of the server? Or I'm missing some configuration?