How to embed a rise course on a gSite with restricted permissions? - a corporate case :)

Dear Fellow E-Learning Heros,

I need your help. I've tried for several weeks and with the help of our corporate support to solve a peculiar problem. We failed.

So what do I want to do?

I want to embed a rise course on a google site. I followed this guide. Everything worked fine.

So what's the catch?

The courses I want to embed shouldn't be publicaly available. It's part of a corporate google site. Instead of giving "allUser" permission we only granted permession to our corporate accounts. That's when the problems began.

When I try to load the index.html I get a blank page, but in the tab I can see the title of the course.
The goodbye.html loads without a problem.

So we thought: Maybe it's problem with the permissions. Changed it back to "allUser" and it worked fine. In the next step we restricted permessions to "AllAuthenticated" and added some google-accounts to test it. Same result as with the corporate permissions:

index.html stays blanc.
goodbey.html loads perfectly.

I suspect the course can't load properly once you restrict permissions, but I don't know why and how to solve the problem. By the way the bucket permission is set to IAM.

Any comments or suggestion are welcome.

Kind regards
Valentin