@stardog,

I honestly do not know why this would start happening, and I haven't tried out Alexa Plus myself yet.

From the sounds of it, the Alexa Plus upgrade is making more heavy use of the device types, instead of your group names. This means that it is seeing the actual devices of type 'light' and only making actions on those devices.

You should consider going into the Tapo App and seeing if you are able to change the device type for each switch to 'Light' which may help Alexa better understand your intentions/commands.

I would recommend setting up a routine in Alexa for 'When I Say 'Turn off all the lights'' > Turn off X Devices.