Switch off the bulb first, then switch it on, wait 1-2 seconds, then switch it off, repeat 3 times or 5 times. Sometimes timing is important. If you did it real fast, slow it down; vice versa.

Does the tplink still work? Can you control lights, plugs... remotely? Would there be any notification or error on Google home app?

Hi, What does it show on the kasa app when that happen? How far is it from your router? If it's too far, signal is weak, and lightbulb might lose connection. Check firmware update on kasa app too.

Reset it. If you still hear buzzing noise, contact tplink support for solution.

Hi, You mean the kasa account confirmation on Alexa app? Or you are trying to register kasa account and link to activate kasa account is timed out?

Hi, Is device time still correct? How did you turn on and off the entries? You may reset one plug, configure it again, to see if problem exists.