@Sebass 

Often 2.4GHz devices regardless of manufature have difficulty connecting on a unified network SSID.  What you can do is disable Smart Connect momentarily.  Connect the devices to the 2.4GHz network and then re-enable Smart Connect.  That should normally fix your concern.  

@Sebass Did that, have 2 networks same name. Still same problem.

During setup, asks for Home setup, scan code on device, then Home never finds the device.

TPLink Archer AX50 and KP125. Seems like this should be a supported option or you would test this. Also failed with an Archer AX 6000.

Looking to buy a bunch of smart plugs and had good experience with the outdoor one I purchased. This is not a good experience.

@Sebass 

Tried totally disabling the 5Ghz network, still no setup.

Went bought several more KP125. Took one at first location with Archer Ax6000, setup worked. Took plug to second location with Archer AX 50, reset and will not join network. Took another new unopened one, still will not join the network. Funny is the KP400 has been working great at either location. 

This is something that should be looked at. Setting up and resetting up a smart plug should not be this difficult. 

Tip - Don't reset a KP125, can not get it to configure again. Will play some more until return window closes, if they don't work by then, they're all going back.

@Sebass Update - after extensive testing with two different TPLink routers/access points and 4 different KP125 plugs, Kasa smart plugs will not rejoin WiFi after initial setup if using Smart Connect. Even tried disabling 5Ghz. Still will not work. 

Returning all Kasa plugs. Tried Wyze plugs, though not HomeKit compatible, and they work easily without any difficulty during setup. 

Going to try Belkin's Wemo plugs next. Would like to try some HomeKit features. 

Curious if anyone can share similar results?

Routers-

AX6000

AX50

Plugs-

TP125 4x