I upgaded all my computers to Spark 2.8.1 (note I am still using OpenFire 3.9.1).
Since the upgrade, sometimes when a user logs in, they appear offline to everyone else (as if they were invisible). You can still message them and they and can still message you, just that their status appears offline.
The problem seems kind of random. Toggling from online to invisible and back to online does nothing. Logging out and logging in does nothing. Closing Spark and restarting it does nothing. Restarting the computer does nothing. But sometimes, for seemingly no specific reason, the next login or the enxt day it will work fine and the person appears online as normal.
Additionally, it seems to happen to some users more than others, and for some users it has never happened.