Having a canonical tag pointing back to the page is not causing a loop.
What our tool looked at two different sites. One has a trailing slash "/" and one does not.
So you have a site that gets linked a lot internally but does not get indexed. Ideally, here would be to point the internal links direct to the site wich should be indexable.
Technically speaking version http://www.domain.de does not exist. The reason for this being each request must always be specified in a path. The smallest possible path is indicated between two „slashes“, „/„. Therefore, the smallest possible path of a domain is „http://www.domain.de/ (same goes for https).
Therefore, Google evaluates the URL http://www.domain.de as it would have a trailing slash http://www.domain.de/. This only is true for the home page URL of a domain and can not be transferred to other directories.
Optimally, therefore, the URL is http://www.domain.de/" class="redactor-linkify-object">http://www.domain.de/ indexable and side http://www.domain.de refers to the Canonical tag on the page with a backslash. Whether there is a trailing slash at the end of the homepage or not, Google indexes both versions and counts them as one.
What is important here, is that all of your internal links are pointing towards the page wich is being indexable, because this would mean, the traffic does not have to use a detour.