Preview mode not working on Firebase hosting

Hi there,
the preview api preview mode is not working on firebase hosting.

We have been working with Storyblok for a while with next.js and hosting various websites on Netlify. A recent project is now hosted on firebase for a client, but preview mode is not working on there. Our development setup on netlify is working fine.
We have spent quite some time debugging but this seems to be an issue only on Firebase.
are any issues with firebase known to cause problems? or any other issues with preview mode on different hosting platforms to consider?
Has anyone else had problems like this?
Thank you very much in advance,
Best regards,
Thomas