Workers with HTMLRewrite not working with web.dev/measure

My website works completely fine, and I am loading under 1s, I have score of 60-80/100 depending on the page. But when Instead of returning this:

    response.headers.set("X-XSS-Protection", "1; mode=block");
    response.headers.set("X-Content-Type-Options", "nosniff");
    response.headers.set("X-Frame-Options", "DENY");
    response.headers.set("Referrer-Policy", "unsafe-url");
    response.headers.set("Feature-Policy", "none");

    return response;

I return this:

const rewriter = await getHeadRewriter("en");
return rewriter.transform(response)

The website dont load on PageSpeed Insights or web.dev/measure. But the website works on the browser and even on the LIghtHouse extension, just not on these sites.

The reweriter only displays a Hello World.

I am thinking maybe “transform” updates the Headers or soemthing. I can’t see for example content-length, and this might be the issue, because I remove the rewriter.transform(response) and works again