"Unknown error" for some websites when running speedlify locally

[Akashic101]

I tried to fork this repo and run it locally and while it did run and I got some results my own website resulted in an unknown error:

{
  "url": "https://www.blog.davidmoll.net/",
  "error": "Unknown error.",
  "sidequests": {
    "-weight.total": 3,
    "+weight.total": 3,
    "-weight.document": 3,
    "+weight.document": 3,
    "-weight.script": 3,
    "+weight.script": 3,
    "-weight.image": 3,
    "+weight.image": 3,
    "-weight.font": 3,
    "+weight.font": 3,
    "+weight.fontCount": 3,
    "-timeToFirstByte": 3,
    "-totalBlockingTime": 3,
    "-largestContentfulPaint": 3
  }
}

ssg.js looks like this:

module.exports = {
    name: "SSG",
    description: "Static Site Generator web sites",
    options: {
        frequency: 60 * 23,
        freshChrome: "run"
    },
    urls: [
        "https://www.blog.davidmoll.net",
        "https://www.11ty.dev/",
        "https://www.gatsbyjs.com/",
    ]
};

Other websites in the ssg.js-file ran fine. I am selfhosting my website using cloudflare tunnel on a Raspberry Pi. Any idea what could cause this?