failed decryption on gwene group?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I sort of doubt this is a gnus problem, but I've seen related
discussions here, and I don't know where else to post, so...

I'm subscribed to the Hacker News feed via gwene, as
gwene.com.ycombinator.news. Recently, opening the group has failed like
so:

gnutls.c: [1] Discarded message[136] due to invalid decryption
gnutls.c: [0] (Emacs) fatal error: Decryption has failed.
gnutls.c: [1] Note that the security level of the Diffie-Hellman key exchange has been lowered to 256 bits and this may allow decryption of the session data
gnutls.c: [1] Discarded message[33] due to invalid decryption
gnutls.c: [0] (Emacs) fatal error: Decryption has failed.
apply: Server closed connection

I'm on archlinux, running emacs-version "24.3.1" and the arch gnutls
package is at version 3.2.3-1.

For a while I had gnutls-min-prime-bits set to 1024 (something I found
from this list), which got rid of the warning on the third line. Then
arch's gnutls package was updated, and I started getting these
decryption errors, I removed that customization, thinking it was the
source of the problem, but now it appears it isn't -- I'm not getting
this error for any group but the ycombinator one, presumably because
it's got this one broken message.

I've catchup'd articles in this group several times, and over various
restarts and refreshes the unread count in the *Group* buffer continues
to be updated, but I can never enter the group.

Is something actually broken in this group's message data? Or maybe
there's something I can change in my setup to fix it? Any hints very
welcome...

Eric