Our goal is to make sure you never miss a message as you move between devices, and today, we have big news for you: This functionality is now rolled out to 100% of HipChat Cloud customers! You will now open your device(s) and see unread messages that came in while you were offline – the way chat should work!
Thank you for your patience as we've worked through this problem.
(HipChat Server customers, note that you can track progress here: https://jira.atlassian.com/browse/HCPUB-2603)
The HipChat Team