@Bat-n-Ball  Hello, 

Thank you for your detailed post, for bulb unstable issue, you could try some suggestions here: 

1.  Please confirm bulb firmware and kasa APP version are up-to-date 
2. Ensure bulb is connected to main router directly not through AP or extenders, Locate one bulb very close to main router and see if it disconnects 

3. You could try to change a different 2.4Ghz wifi channel on router and see if that helps 

4. Turn off Advanced wireless settings like WiFi optimizing Band steering etc. 

If the above does not work, can you help confirm some information to locate the issue: 
1.  Your network topology ,e.g. Router  Netgear XR500 (in living room) <wireless> KL130 ( in living room) 
2.   MAC address of the bulb (please share via private message)
3.   Can you access the bulb locally when phone is connected to home wifi when the issue happens? What is the Error you got when bulb disconnects? 
4.  Signal strength of the smart Bulb on the APP: Kasa APP, go to device  settings->signal strength ( tap on the Wi-Fi icon/ SSID to see the value of the RSSI)
Thank you. 

@Bat-n-Ball Thank you taking time responding the case details.

I have added them in the case note and escalated your case,  our seniors will look in the issue and follow up via email.