I have also had this happening occasionally as of late…
It only has happened since turning on LDAP authentication, and simply getting the affected user to log out & back in seems to solve the problem in the short term.
The user can log in… everyone appears as offline to them… and they appear as offline to everyone else… But I log into the server console and can see they are actually connected.
I have a support ticket lodged with Jive about this (running Wildfire Enterprise 3.0.1)