I have seen this situation too. One day I can say to my phone, "Hey Siri, turn on the foyer light." and it will work just fine. Another day and the command won't work--without me having changed a single thing in the equation. Moreover, I can invoke the same command using Siri on my MacBook and it will work (even though it simultaneously won't work on my iPhone.)
After researching this, I've found two things that seem to resolve the issue.
- Add specific shortcuts to via Shortcuts.app to invoke the Home.app action. This has worked in the past, but I can't confirm that it will always work.
- or - - Completely disable Siri on the iPhone, wait a while, re-enable it (including all the steps to get it to recognize your voice), wait a while, try command again.
I don't know why Siri would be getting into a bad state on the phone other than an iOS issue (especially since it has never not worked for me on the laptop). I don't believe this has anything to do with HKB.