What the devs said was, that the latest version of Unity started bugging out Shroud, the plug-in they use for cloaks, which in turn caused cloaks to stop rendering on mac. That means it's a Unity problem, and I'm sure they've already brought it up with Unity support and are simply waiting for a clear reply / solution so they can relay it to us. It certainly doesn't sound like a problem that Obsidian can fix by themselves, and however much we spam the forums, I doubt it'll make the Unity guys work faster (they probably don't read Obsidian forums specifically considering the amount of other studios they have to support).
Apologies that I can't quote what the devs said exactly, but if you want, I'll try to find it.