I had same issue when it was connected to my extender. Either my wifi extender didn't like TP-Link device or vice-versa. I removed the device and installed again connecting directly to my router, and...

@ilovepancakes I had the same issue. For some reason the switches didn't like my extender. When I changed to my main router they work just fine. So, definitely an issue communicating with your wifi...

@Carl I was having the same issue and found this work around: https://community.tp-link.com/us/smart-home/forum/topic/222218 Seems like you have to reserve the MAC Id for the switch/plug. Good luck.