Seafile Server 8.0.3 SSO (shibboleth) not working

Shibboleth SSO integration stopped working after a upgrade from 7.1.5 to 8.0.3.

When I use the [Single Sign-On] link the first time I get redirected to the shibboleth mask. I can also tell from the shibboleth logs that this step is successful.
Instead of logging me in my seafile account I end up back on the login page. Further clicking on [Single Sign-On] simply reloads the page.

I’d love to provide more detailed logs, but unfortunately there are none (except apache access logs and shibboleth). I tried to enable more verbose information as described in: manual seafile com/deploy/shibboleth_config_v6.3/
But unfortunately there is no change in verbosity.

Anyone else using 8.0.3 with shibboleth? Is there a way to get more debug information on what is going on during the auth process?