For those that use IRC software - Slack, HexChat, MatterMost - what issues do you normally have with the user interfaces?

I haven't tried Discord yet. How would you compare it to Slack or MatterMost?

Haven't tried MatterMost but they're for different types of users. Discord is for general communities a la IRC. There are built-in voice channels so you can hop on an audio conference by simply joining the voice channel. You can use a single account with different nicks for all your channels. Large subs on reddit have introduced Discord channels.

Slack has hundreds of plugins for enterprise environments such as notifications from Jenkins CI and direct access to Jira for issues. It requires group association before joining an org but once you're in, it's like an intranet environment with fewer restrictions.

SPC (Join to see), since I wasn't "mentioned" in the comment above, I wasn't notified. Excluding the ability to change your nick per channel, MatterMost and Slack allow much of the same features. I hear the biggest marketing point for Discord is their respect for privacy.