Hello @Giovanni1975 

Sorry for the late reply.

• If only one of the smart plugs could not be controlled by Tapo APP, you could factory reset and set it up again on Tapo APP.

How to factory reset the Tapo smart plug 

• Make sure device could be controlled in Tapo APP remotely ( phone is on LTE or different network) first. 
• Then try to Disable and Enable Kasa skill, and relink your Kasa devices in Alexa app as the guide here: (skip this if you've tried it)

How to use Kasa Cam with Amazon Alexa

Please help provide some details here if the above still does not work

1. Can you control the device locally (same network) from the Tapo app
2. Can you control the device remotely (LTE or different network) from the Tapo App
3. Try to manually control smart device in Alexa, is there any Error, please share a photo of error
4. What Alexa did say to a voice command and the more exact time : e.g. 9:00AM, ' Alexa, turn on bedroom lamp' , Alexa responds ' ...

Can you share the Mac address of plug which could not be controlled in Alexa/ Google ?

Thank you