Hey @Graykenhill
I have confirmed it with the development team that this is not a feature, but a bug (at least in this and previous beta softwares).
I have also put an emphasis on analyzing this particular problem, as it seems that only some users are affected by it.
I just want to confirm this, since that is what I have told the development team 🙈
If you go to Settings > Lock screen > Always on Display > Auto brightness option is turned off, correct?
And @Awahwah
If you haven't already, then please be sure to share an error report via Beta Feedback option in Samsung Members app, with a description of a problem (how exactly do they not work, what is a problem and how is it different from the previous beta binary) 
