Performance custom metric `is_lcp_statically_discoverable` is incorrectly reporting `false`

[kevinfarrugia]

Test URL: https://webpagetest.httparchive.org/result/221228_GY_1/1/details/#waterfall_view_step1

The LCP image is https://marieefleurir.com/html/template/default/img/top/firstviw01.jpg and is included in the initial HTML document sent by the server. I understand this should be recorded as is_lcp_statically_discoverable as true.

The root cause seems to be because raw_html: {}, which in turn is caused because WPT_BODIES[0].response_body: null.

See test: https://webpagetest.httparchive.org/result/221228_9S_4/1/details/#waterfall_view_step1 which includes custom metric:

[01_test]
const response_bodies = $WPT_BODIES[0];

return ({
  response_bodies
});

Is this a known issue? Why is response_body body null?