@Hugh2 

If Kasa works fine, and you already re-linked the skill in Alexa, it would be best to have Amazon support look to see what could be happening. 

Alexa relies on the remote control in Kasa to control the device so if the app is working something in Alexa is not.

@Hugh2 Did you get it to work? Mine just stopped working as well.. i can control the plug from alexa app and can turn on/off manually but voice commands stopped working all of a sudden

Hugh2 wrote

Plug works with both the KASA and Alexa APP, but not Alexa voice commands.  Working for about a year and resently stopped.  Both on same WiFi network.   Tried deleting and re-installing in both apps, disabling/enabling skill.  Still no Joy.  Idea's?

@Hugh2 i figured out mine.. My Alexa had switched to my wifes profile.. when i switched back my own profile it was able to control the devices..figured i'd share it in case someone else has multiple profile/household setup in amazon/alexa

@Andy321My internet provided changed the gateway? Now my voice commands to Alexa don't work for my smart plug and I cannot connect my smartplug to the internet with the kasia app.  What do I do? 

@MWoods  Changing the default GW shouldn't have affected the smart plug.. If all your other devices can access the internet then it's probably just the smart plug that needs to be reset. You can probably find instruction on how to reset it to factory default and reconfigure it again

@Andy321 I checked and both of my Alexas are on the same account and all thre TP-link Kasa plugs (all the same) are responding manually in both Kasa app and Alexa app but when I ask Alexa to turn on one plug it says that plug doesn't support that.  

@LArndt Maybe you just need to disable enable the skill

sign into you amazon account and then try disable/enable the skill. 

https://www.amazon.com/TP-LINK-Kasa/dp/B01EIQX6Y8