Okay, just tested it again.
Taint log - just in case you want it.
Anyway; disabled all the addons I've added on top of RealUI and it still threw the error. Then disabled !Aurora_RealUI and... it still threw the error. After that, it asked to disable Aurora, which I did, and then I was unable to produce the error at all - abandoning or having the quest prior to reload.
So, now you may beat Haleth with a banana.
