@Banjomaniac,

I think you first want to try and discover whether it is a hardware behavior or a software behavior. It could be something as simple as an integration automations erring and causing the automation to flash the light, or automatically turn the light off immediately. In the app, did you see the light switching on or off?

First check your automations and device history to make sure that you did not accidentally create an automation in the Tapo App, then check the other apps that you can control the switch from. You may also simply try factory resetting the device with a different name to try and break any connections or automations that could have caused the behavior.

It could also be the result of a potential leakage of power between your wires/lines. Make sure that your connections are all secure and there is no possibility for power to jump between wires. Lastly, try estimating the length of wire that runs between your switch and light, in longer runs it is not uncommon to see odd behaviors due to the power needed to make it to the light being increased.