Mixed content error

[tmechsner]

What I'm trying to achieve

I've been playing around with saleor a few days now and come across diverse errors in a production-like test setup. The build process works fine and running backend and storefront locally works fine too. However, in the production-like setup, the storefront sends requests to "https://my-domain/account/". The response header includes Location: http://my-domain:8080/account/ which results in the following error message in the console:

Mixed Content: The page at 'https://my-domain/service-worker.js' was loaded over HTTPS, but requested an insecure resource 'http://my-domain:8080/account/'. This request has been blocked; the content must be served over HTTPS.

And then, probably related to this:

Uncaught (in promise) TypeError: Failed to fetch (service-worker.js:1)
Uncaught (in promise) DOMException: Failed to update a ServiceWorker for scope ('https://my-domain/') with script ('Unknown'): The object is in an invalid state. (my-domain/:1)

In my local setup (running with next dev) the storefront landingpage does not send a request to "/account". Why does it do so in production?
No configuration anywhere uses non-secure "http" and no configuration anywhere contains the "8080", except for the nginx configuration.

Steps to reproduce the problem

Deploy the latest 3.0 Version of the backend and the storefront via docker (build with github actions, deploy to sloppy.io), load demo data, go to the storefront landingpage.
The Dockerfile is almost identical to the original one, except that nginx is configured to listen on port 8080 which is then mapped to port 80 in the hosting setup, and the nginx server_name has been adjusted.

What I expected to happen

No errors in the console.

System information
Browser and OS should not matter here, as in a local setup everything works fine.
The production-like test setup runs on sloppy.io (docker hosting).