Can you please confirm which Linux client version you are running on? I connected to my HipChat Cloud account using 126.96.36.1990 on Ubuntu 16.04 to reproduce this problem but did not run into this issue so far.
A new server was recently added on HipChat Cloud side. The URL is likeabosh.hipchat.com and some users are still being requested to trust this certificate manually. If you are being prompted by this pop up, you can trust the certificate and be able continue to use the application normally.
I have deployed a brand new 17.10 on my end but I did not encounter the issue so far. Is this your first time running HipChat on this machine?
Additionally, please provide the output of the command below so I can compare the list of certificates that you have with mine.
As a temporary workaround, I would suggest you to use the web client if the pop up is causing inconvenience to you.
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event