I was ready to return my 3 pack of dimmer switches and I even had a return authorization from the TP-Link representative I chatted with.  But I tried once again over the weekend to get them working before I sent them back.

The problem:

The two HS220 dimmer switches that I installed were functioning perfectly before I used the Kasa app to connect them to WiFi.

I turned of 5GHz on my WiFi router to make sure it wouldn't interfere, just for the setup.

Adding the switches in the Kasa app failed and left the switches inaccessible.  They did not function manually either.  Factory reset did not work at all no matter what I tried--pressing the left or right bottom buttons for various amounts of time and in various orders.  This meant I could not start over or try anything else because they were in a failed state and could not be factory reset. I was prepared to return them.

If you are in this situation, here is how to fix it.

@gotliebk wrote that the factory reset would work if you first turned off the WiFi that the switch was connected to.  In other words, as long as the switch is connected to the WiFi that you entered in Kasa (even though it failed) it would not allow a factory reset by pressing on the left button below the switch for 10 seconds.  The minute I turned off the WiFi, I was able to do a factory reset by long pressing the lsft bottom button. The switch started blinking green and orange again -- setup mode.

The firmware needs to be updated and you can't do it through the Kasa app in its broken state.  So you have to do a manual firmware update.  Download beta firmware from this thread, post #11: https://community.tp-link.com/us/smart-home/forum/topic/240976

Download the new firmware files and unzip to your computer. In the folder IoT_UpgradeTool_For Windows/Mac, you will find a file called main

If you were able to reset the switch to factory default, it should be blinking orange and green.  This means it is putting out a WiFi signal.  Search for the wifi signal with Kasa in the name and connect to it with your computer.

Now run main.  Select Scan, and it should find the switch.  Now press update.

The update should complete but your computer will reconnect to your normal WiFi as soon as the switch reboots.  The update will seem to fail -- even if you are quick and reconnect to the same Kasa signal.  But it has, in fact, been successful.  You can test this if you want by repeating the firmware upgrade.  This time, when you tell it to update, it will refuse and say the firmware is already up to date.

Now you can connect through the Kasa app.  For me the process was now successful.  As soon as the setup in Kasa was complete, it prompted me to upgrade the firmware.  I was apprehensive, thinking that the upgrade might actually put it back in an unresponsive state, but I allowed the firmware upgrade.  This installed version 1.0.8 and it continues to function well.

For what it is worth, I activated a guest network on my router and named it Kasa, limiting it to 2.4Ghz.  This is what I connected to.  I would rather not have the switches on a separate network, and it is probable they would have worked on my normal network.  I will probably change this back at some point, and I read that the Kasa app now allows you to change the SSID of the network without having to reset the switch and start over.  When I feel brave again, I will try this.  But for now, all is working, and I am glad I didn't return them.