So why does the Event Hub show it when a friend/guildie has "An unexpected error occurred on the server"? Just... why? Why do we need to know? Why is this "event worthy?"
Event Hub: Unexpected Error on the Server
How are we supposed to know if something is a glitch or not, especially if they don'f fix it?
I've also seen it show up now when a friend/guildmate reaches certain ranks, I can't remember which but might be when players gain access to T2 or T3. Also a bug.
The game tries to access invalid parameters when getting T2 and T3 clearances, and getting clearances for Shadow Lairs and causes that error.
@Hollows
If something isn't fixed in time, it becomes a feature. Unexplained errors are a feature until they fix them. This is because like Orbwanter said, no one is being hurt by this and it doesn't really matter.
The other big reason is that clearances may be useful in a newer update, and the bug will fix itself when beating all of the shadow lairs becomes relevant to something.
Someone beat Darkfire Vanaduke, and it tried to award a fourth Shadow Lair clearance that doesn't exist. Old bug they haven't fixed because it's harmless and they have higher priorities, I guess.