Some servers cannot be connected to; Polari doesn't say much about why. Invalid SSL certificates?

In particular, I'd like to connect to irc.7chan.org on their secure port (6697), which uses TLS1.2+AES256. This server works with other clients such as irssi and xchat-gnome. Polari claims it cannot connect due to a "network error" but does not specify the nature of the error.

Based on https://www.reddit.com/r/gnome/comments/3pfymf/what_am_i_doing_wrong_please_help_polari_arch/, I'm tempted to think the cause could be an invalid SSL certificate--however Polari now connects to irc.gimp.org and I am not sure if they updated their certificate or if a fix was implemented in Polari.