@Wayne-TP 

Thank you for your swift reply. Much appreciated

I have seen and experienced lots of issues but this one is weird.

All four KASA lamps went offline at the same time.  I can see through my cameras that ALL KASA lights are ON - day and night without changing.  Since they are offline the schedule function doesn't work.

There has been no general power drip in the house.  I get remote warning if that happens.

Each of the lamps is connected to a different circuit and 3 of them are close to the router.  The network works perfectly, both TAPO and ARLO cams work very well.

The router is rebooted at regular intervals to guarantee optimal signal reception.  This causes all device to go off line for a minute before connecting back.

You must be aware that the TAPO app was updated and now also can manage KASA lamps.  Could that possible have generated a glitch pushing all KASA lamps off line ?

Have you recently seen a surge of KASA lamps going off line?

You mention manual reboot in your suggested solution. Do you mean, just cutting the power to the lamp one time and "on" it again ?  or waiting xx seconds.  I cannot ask a stranger to disconnect the lamps from the network through a factory reset and reconnect the lamps to the wifi network but i can ask them to swith off and on the lamps.  Please advice and let me know what you think about my TAPO/KASA thinking.

thx, bruno