I've been successfully using three HS103 plugs with the iPhone app without a problem so I decided to order a 4-pack and add more of them. I have been unable to do so. I go thru the app to add a plug (+) and it will not recognize the new SmartPlugs. I've done a hard reset, I've forgotten the SmartPlug, I've verified I'm on WPA2 and I've shut off the 5gHz radio in the router. The app sees the SmartPlug wifi, the app sees my network but I have to tap Join 3 times to get it to progress but it never establishes the final connection, it never switches back to my network. The indicator continues to flash Orange/Blue.
I've turned off BT & Cellular, tried Airplane mode, and WiFi only, no luck. There are only 4 devices on this Unifi WAP network, two of the existing SmartPlugs are on another wifi network but I can control all three. The only options for encryption are WAP2 or Open. I've also moved the plug to the opposite end of the building to be clear of other wifi devices.
The problem ended up being NORD VPN. Even though it showed off and on a trusted network, it still interfered with the with the setup. Once I deleted the configuration IKEv2 from the iPhone setup menu, everything connected as it should. I'm leaving this up for general knowledge, if you have a VPN setup on your phone, disable/delete it from the setup menu then reconfigure from the app once your devices are connected..