To be fair Slack doesn't do this and other network related things much better (in my experience). For each complaint here about HipChat I experience the same failings in Slack, just less often. But Slack is a bit better, so people make the argument that it adds up. (We moved from HipChat to Slack several month sago, I didn't find it much of a game changer apart from getting the company to pay Slack to store history and make it searchable but I'm someone who would be content with IRC and searching local logs.)

I actually raised a ticket for this.

There was a long thread I didn't follow at all about how that was how it was supposed work.

That's when I switched to Slack.

That’s the best case.

It often fails to notify of new direct messages, I suspect thinking one device was active when it was received.