First time I went to look for it - left because of the issues others reported after 10 minutes.
Second time I went, it was there and I killed it.
People are having issues, yes. Just go about the game and try it only when you can accept failure (because failure is highly likely atm) that it wont be there.
The boss was actually detected by my Companion (and was shown on the compass) yesterday, she kept firing arrows in the direction for about 15 seconds before giving up.
Yes, there are already several threads on this boss, one including a dev comment that it will be fixed in the next incremental and a possible workaround:
Issue:
You are in combat and Boss cannot be seen, companions react to boss that cannot be seen.
Fix:
1. Ensure you are not in combat. Head back to Inner Caverns if you have to get out of combat
2. Log out, then log back in.
3. Enter boss area.
4. If not fixed go to step 1