Thanks, tested on 26.1. Works a treat! :)
Thanks for the prompt reply Peter! Much appreciated. I actually hadn't even realised I'd upgraded Emacs along with a bunch of other packages, and spent some time in mild confusion :) "How did this work yesterday? What's changed????"
ps-ccrypt broken on Emacs 26.1
They're defintiely not going to be fixing it :( Thank you for your reply, and I'm very sorry to hear that the XMPP gateway doesn't work. We're not actively developing the gateways at this point, unfortunately. Therefore, the behaviour will not change.
It looks like the Slack folks are well aware that their XMPP gateway isn't standards compliant. Jabber clients and our XMPP gateway are not necessarily handle everything strictly according to standards. So it's quite hard to call up a list of channels, and the best way to join them in Jabber is to use roomname@conference.name.xmpp.slack.com and sign in to them individually. We're not actively developing the gateways at this point unfortunately. Sorry I don't have better answer here. Please do let...
I have raised a support ticket with Slack, and directed them at this bug. I'll post any updates here.
I think this is related to: https://emacs.stackexchange.com/questions/13899/connecting-to-slack-channels-with-jabber
Slack channels not appearing in *jabber-roster* after signin