This quest certainly does seem broken in interesting ways.

My current predicament: Played hide and seek with Oliver before talking to Art, woke Art up and got Halsin to recover Thaniel, but in the Oliver fight with the shadow shield, managed to directly attack the shield and then Oliver (rather than only attacking shadows to burst the shield). After the shield popped, seemed like Oliver body jumped or something to one of his shadows, but no dialoge ever started, and after this fight, could not find Oliver anywhere despite the quest marker at the cabin. This was all before completing Shar's Gauntlet and Moonlight Tower.

Figured it was just bugged beyond repair and continued on, however after Moonlight, suddenly got he option with Halsin of "Oliver's immortal", after which the "Shadow Cursed Spirit of the Land" (not Oliver) is suddenly back above the Shar monument in the middle of town. The spirit seems to be permanently hostile, summons the same 1 HP shadows, and never forms a shield. I've tried dominating, charming, killing legions of shadows to break a shield that wasn't there, but can't seem to ever get a convo to start.

Anyone else seem a similar set of circumstances, or managed to get a successful resolution? I've about hit fuck it and am just going to move on to Act 3, Halsin be damned.