@marcel Sometimes the platform you're deploying to adds (or removes) the trailing slash—I know this kind of thing happened to me at least twice. But it looks like you're using a static site—it could also be the live reload server vs static (built) page.
So, one thing I would try is running astro build locally and then serving the dist directory locally (i.e. by cd'ing into it and running python3 -m http.server 8080).