I would like to report a bug.
I killed Illidan after the reset on my Demon Hunter and I encountered a bug, when after killing the boss no loot has dropped. I was not locked to this boss before.
I think the boss was killed with the Throw Glaive ability.
More information would help, such as buffs and talent modifiers for the specific ability.
This should not get discredited so easily, especially after last week’s reports of Mage Flurry spell resulting in the same behavior by one shotting legacy content bosses with a hard-cast.
I saw some comments on Reddit that if you kill Illidan too fast before Maiew gets the killing blow no loot will spawn. I haven’t tried to run the raid myself so I have no idea if that is accurate or not.
Best idea probably to attack slowly, unarmed etc.
Hey Beeyourself,
We are aware of an issue with Illidan at the moment. While we wait for the developers to fix this issue, it looks like you can receive the loot if you try again - just make sure that he finishes his dialogue with Maiev before killing him.
Hope this helps. 
Had a similar experience with frost mage’s flurry on Ultraxion.
It’s not just Illidan and bosses with some kind of mid-fight roleplay or multiple phases of damage immunity and this is happening to Hunters one shotting with Barbed Shot as well. I’ve also seen complaints about Attumen and Ultraxion.
The common theme for problematic spells is a fast projectile with an additional damage of time component and a specific circumstance where the target dies so fast you don’t even see a single tick of DOT occur.
Having the same problem with Blackhand