Areelu fight...random Arcane check?

I don’t if this is a bug or not but it feels like a bug. I have fought her many times and I randomly get an arcane check after beating her the first time. I can pass the check and bypass having to fight her clones, but after happening a few times the check stopped being available.

It’s a difficult check (DC 50) but why does it only show up every once in a while?