Errors when running "normal" Matomo and Tag Manager on one Site (V3.10.0)

When I run “normal” Matomo and Tag Manager an one Site, we have some errors in the tag manager:

  • The first tag is not getting to the matomo server (Not at all)
  • when some other tags are hit the error message “Error: A siteId must be given to add a new tracker” appears
  • in the preview-mode everything works fine
  • When I only run the Tag Manager it works fine too.
    What can be wrong?