Yes–custom DTH. I mentioned it at the bottom of my initial post:
I just tried it with CoRE, and sure enough, same problem with the same log entries! It has to be the @infofiend DTH. I’m not quite sure what it’s expecting, although this “feature” is stated in his thread:
It indicates that he converts those HSB values to xy before sending to the hub. So it does seem like to me that the @infofiend DTH is miscalculating the transform’s leading to the invalid xy coordinates being sent to the hue hub? I sure hope his RGB transforms are correct.