Has anyone else had issues with Siri since upgrading to iOS15.4?

I don't use Siri for much, but have been making use of it for controlling smart home lights through Home Assistant, and until today things were working very smoothly.  Now, when I use a command like ""turn on the hallway lights", instead all the lights are turned on.  Other commands aren't even recognised at all.  I wondered if this was a back-end issue (something to do with Home Assistant) or with my phone, so for comparison, I tried issuing the same commands using the remote for my Apple TV 4K, and they are working fine so it seems like I can rule out Home Assistant as the problem.  That just leaves my iPhone running iOS 15.4

I've tried a bunch of usual fixes (turning off/on the device, deleting Siri dictation history, re-training Siri, but nothing has made a difference.

Anyone had the same experience, and maybe come up with a fix?