Does anyone have an actual technical theory of how it’s possible for commands that used to work , say a month ago, to just stop working?

What is it about Siri’s architecture that causes “Set bedroom light to 30%”, a command that worked for years, to randomly stops working on a random Tuesday with no OS update or home change?

I mean, what on earth are they doing on the back end…?

For me, the standout was a period of 6 months or so when Siri stopped understanding the world "half" (as in "lights to half"), and thne it abruptly started working again.

My hypothesis is that when Siri does processing on the phone its abilities are severely diminished. Perhaps there is some heuristic it uses to pick if it processes voice to text on the phone vs on the server (e.g. possibly based on server load). That might be why you see inconsistencies day to day.