So I build my project with output: standalone option with npm run build
Then I copy .next/standalone into a docker image created from node:16-alpine
However, when I start server.js and open it from the browser, it returns 500 Internal Server Error and prints this in the console:

Listening on port 3000 url: http://480ba79a78f0:3000
- error Failed to handle request for /
TypeError: fetch failed
    at Object.fetch (/app/node_modules/next/dist/compiled/undici/index.js:1:26669)
    at processTicksAndRejections (node:internal/process/task_queues:96:5)
    at async invokeRequest (/app/node_modules/next/dist/server/lib/server-ipc/invoke-request.js:21:12)
    at async requestHandler (/app/node_modules/next/dist/server/lib/start-server.js:336:33)
    at async Server.<anonymous> (/app/node_modules/next/dist/server/lib/start-server.js:152:13) {
  cause: Error: connect ECONNREFUSED 127.0.0.1:33593
      at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1278:16) {
    errno: -111,
    code: 'ECONNREFUSED',
    syscall: 'connect',
    address: '127.0.0.1',
    port: 33593
  }
}

What is going on? I don't have an idea what it is trying to do: why is it connecting to localhost:33593 for example? Why it can't fetch even the first page? It worked before on Next 12 projects.