Arelith

Title says it all, they're all invisible!

For me it is intermittent, but when they are invisible, they are invisible for the entire party.

It happens if you cross a server transition after you've seen a pit fiend somewhere (this happens notably quite often with PC summoned pitfiends). On the new server, you won't be able to see them until you restart your game. Similar bugs happen for player head models. Very annoying!

Regularly occurrence - including from my own Gate summon.

I have not yet identified a root cause for this one. That it's intermittent is annoying in itself, but issues related to server transitions are especially more difficult to isolate than those which can be confined to one server.

Pit Fiends are not the only creatures that use hak models, but I imagine they're the most common victims of this bug, what with the Benwick/Last Bastion transition. Can't make any promises on a timeline but this one has definitely been on the radar.

The 'invisible enemy' bug also can happen to any monster/NPC. And has been around since before haks.