Alexa scene activations all responding with "doesn't support that"

Hey folks - starting a day or two ago, suddenly Alexa doesn’t seem to be able to activate any scenes that have been working forever. I have a scene called “night mode” that simply turns off all the lights in the house, and now my voice command of “Alexa, turn on night mode” causes it to respond with “Night mode doesn’t support that”. Literally, this (and other scenes) have been working for years, and they suddenly are not. Any ideas?

Activating the scene directly via the smartthings app works fine.
Controlling the lights individually via Alexa works fine. As does controlling a room “Alexa, turn off dining room.”