TYPO3 Core

Hello,
i have to modify the canonical tag. I do this thru the ModifyUrlForCanonicalTagEvent.
But after cache it always keeps the canonical url from the first cached page. Maybe additionalHeaderData in general is affected.
Don't know its a bug or i am using something wrong. The PageTitleGenerator works fine.

services.yaml
NS\MyExt\EventListener\CanonicalListener is called only once. Looks like route arguments below not respected in the cache hash?

services:
  ....
  NS\MyExt\EventListener\CanonicalListener:
    tags:
      - name: event.listener
        identifier: 'ns/myext/canonical'
        after: 'cs-seo/canonical'
        event: TYPO3\CMS\Seo\Event\ModifyUrlForCanonicalTagEvent

Site config.yaml
Looks like the my_ext_item_slug argument will not respected in the page cache hash?
This probably where the problem is. But why?
(I am using the Simple type because the data are fetched from an remote rest api)

routeEnhancers:
  MyExtItemDetail:
    type: Simple
    limitToPages:
      - 1047
    routePath: '/{my_ext_item_slug}'
    requirements:
      my_ext_item_slug: '^$|[a-zA-Z0-9-].*'
    _arguments:
      my_ext_item_slug: my_ext_item_slug