@RichardO 

Maybe a range or other network issue causing the device to drop / reconnect.  I replied about a similar issue,and also found having the Kasa app open seems to contribute to the issue.

ITry closing the smartphone app and see if your switch chows up again.   If not.. make sure you have good range and the device is not binded to any access point.  It may be losing its connection trying to switch between two access points..  but in my case binding made things worse.