They were in contact with the CEO. They had some problems since they wanted to send out an email to all 42k participants with an invite link. Apparently invite links for Slack are only valid for up to 2k users.

It seems like the Slack team was able to help, but they didn't disclose how exactly [1].

[1] https://twitter.com/WirvsVirusHack/status/124104522882975334...