Seems to be a worldwide problem. A user on Reddit says Amazon, Germany, knows about it and is working on it. I'm guessing they didn't do a very good job of quality control testing.
The glitch seems to be a problem with group recognition. If you have several devices in one group, such as "bedroom", you can work around it by saying, "Alexa, Bedroom off". When she asks "Which device", say, "all". Somehow they disconnected the concept of a group name and all the devices in that group. But I think they may have also screwed up the distinction between the Alexa device grouping "Lights" and any user-defined group or device that contains the word "light".
Interestingly, the glitch only showed up in rooms with only Hue lights or only Leviton switches. My living room has 1 Hue light and 3 Amazon smart switches. They all work as expected when I say "Living room on".
I'm hoping they get this one figured out soon, clearly explain the naming rules and implement better QC procedures in the future.