Middleware cant be found in V2.8.8

I have updated my Traefik instance from 2.7 to 2.8.8 and now my middleware doesn't work anymore. I get the error:
level=error msg="middleware \"hsts@file\" does not exist" routerName=site@docker entryPointName=https

I have declared a label in my docker-compose file:
- "traefik.http.routers.site.middlewares=hsts@file"

My config.yml file looks like this:

        sslRedirect: true
        stsPreload: true
        stsSeconds: 315360000
        stsIncludeSubdomains: true
        frameDeny: true
        contentTypeNoSniff: true
        referrerPolicy: "same-origin"
        permissionsPolicy: "camera=(), microphone=(), geolocation=(), payment=(), usb=(), vr=()"
        customBrowserXssValue: true

Other *.yml in the directory are parsed, so Traefik sees the files and applies it other files. So only the Docker images don't seem to work. Am I making a mistake in the label?

Turns out that I made a typo in another file. So the YAML-file wasn't parsed correctly.