Now I can guess..
It was a free site hosted on https://www.lima-city.de/
the hosting website is still online https://www.lima-city.de/ and I think it is the hosting company that took that page offline.. still don't know why?
The only thing I can notice is that it promotes communist books. but that should not be a reason (I think)
I can confidently say that that reason for the page been taken off is because the site promoted communism.
Is it illegal in Germany to promote communist ideology?
This is part of their site's menu of content.. none of the links is working because they all hosted in the same hosting company.