This sort of thing happened with Season of Mastery (the initial season) as well.
We did get an explanation via Twitter of how there are variables that are created for the seasonal servers, for example, that are supposed to be “hidden” for Era (and now for HC as well) but sometimes mistakes are made and those changes bleed over.
These are just a few off the top of my head and courtesy of threads I’m watching.
I realize that the bg thing isn’t really germane to HC but it is an example of things misfiring.