If Lucifer still holds onto one core concept, it's that he's problematic.

That, of anything, is unlikely to ever go away. But the definition of it may change. He can definitely be problematic for other, non-revenge and backsliding reasons.

He retakes his seat because Istredd isn't the only one who needs rest now. He only grunts in response to Istredd making his life more complicated. Yeah, he has. But. Lucifer will figure it out. Later, if they get through these negotiations unscathed and return to Thorne.

Not really. Kept Jack from sleepwalking off the boat. That's about it, thankfully. For now.