Maybe my obsession with this message in the logs… it’s what makes me blind on how to solve it.
At this point of the problem… let me ask you @Aleks a question… Do you recommend for the sake of my sanity, to f*ck it up, delete the server, and start from scratch?
As a developer of the project, i’m generally speaking against the idea of “solving” issues by reinstalling everything, it could still be an issue related to your browser or network setup and you may still encounter the issue even after reinstalling. But could also be an issue in the code, idk
May I suggest that you open the debug interface in Firefox with F12, inside the Network tab, then go to your admin, try to log in, and let’s check that the “POST /login” request does come with a set-cookie header, and that the following “GET /versions” request does come with a cookie header containing session.yunohost.admin (NB: in the request header this time, not response header). Cf screenshots below: