I have a feeling a few key beta readers have left in the last few years the ones who really pick up on tiny things.
I think that might be the case. I noticed a scene in the lab in 12M described the summoning circle as fire-ruined copper. There were a couple of upgrades to the circle in previous books ... IIRC by Changes it was some complex mix of metals that he'd had to subcontract the svartalves to make.
Reverting that doesn't seem like a clue, it just seems like he's shorthanded on betas with a memory for details. Or else they themselves are also in the same trap of seeing so many drafts that they forget the published one.