Ever since upgrading to Jabber 10.5 (and CUPS v10.5 after that), some (quite a few) users show up as offline even though they are signed in and functioning fine. We've checked firewall settings, changing how they log in and reviewing account setup, but everything seems fine. Looking at their profile in Jabber (Right-click > View Profile) the offline accounts look identical to online accounts. Look at "jabberofflineexample_a.png" for what it looks like from Person A's chat window.
Bug in Jabber or....?
TAC could never really figure it out. To work around it for the users showing up offline, you have to manually set their Presence server back to their primary one.