Connection refused for index.htm from Gatsby static files

I have deployed a Gatsby site at This site includes a bunch of static HTML files, some of which are called index.htm.

When I try to access these, e.g., 17.03.2024 Kin. D Standard, the connection is refused. Other static files, e.g., 17.03.2024 Kin. D Standard can be accessed.

Why is that and how can I fix that?

UPDATE: The file is actually accessible, and the issue is related to the use of an IFRAME, which I have no control over, as the HTML is auto-generated. In particular, the X-Frame-Options: Deny HTTP-header is breaking things.

I solved it using these two resources:

I added the following to my gatsby-config.json:

headers: [
    source: `/events/*/*/*.htm`,
    headers: [
      { key: 'X-XSS-Protection', value: '1; mode=block' },
      { key: 'X-Content-Type-Options', value: 'nosniff' },
      { key: 'Referrer-Policy', value: 'same-origin' },
      { key: 'Content-Security-Policy', value: `frame-ancestors 'self'` },