Gwene: feed exists but doesn't?

Hello,

I wanted to add the feed at

    https://blog.seamonkey-project.org/feed/

Gwene suggests the group name gwene.org.seamonkey-proj.blog, which I
accept, and then it tells me

    "This group name is already in use for
    https://blog.seamonkey-project.org/feed."

So I tried to subscribe the group, but Gnus tells me

    "gnus-select-newsgroup: Couldn't activate group
    gwene.org.seamonkey-proj.blog: 411 No such group
    gwene.org.seamonkey-proj.blog"

Is there anything I can do?

(I believe it isn't the first time I see something like this.)

-- 
TIA,
Nuno Silva