Thank you @testbird for the hint. I think I have tried Jami when it was still called “Ring”.
I haven’t dug to deep but I am afraid they do share my point of view 
As much as we like to say that Jami is completely without server, sometimes it is not exactly right as we have seen.
(From Establishing peer-to-peer connections with Jami).
In the settings there is a bunch of server URLs for various peer discovery techniques. I haven’t found too much about their contact discovery but there is at least one issue that hints a central service.