I currently use the Harmony Hub (Logitech) paired with my Alexa to control my TV with voice commands.  A couple weeks ago, it quit working. So, I tried the basic stuff: power cycle the hub, power cycle alexa, even tried disabling the Harmony skill and reenabling it.  (I DID notice that I could control the Hub just fine from my cell phone, but that defeats using it through Alexa, so it accepts voice commands.) All to no avail.  This is how I fixed it.

Exit the Harmony app on your phone completely by force closing it. Clear the application data – this will make it so it’s like you’re setting up a brand new hub when you re-open the app.

Uninstall the Harmony app from your phone, and reinstall it.

Unplug the Harmony Hub. Before re-plugging it in, hold down the pair / reset button, then re-plug it in while holding the button down. Continue to hold the button down for 5 seconds and the hub should start flashing rapidly red. After about 30 seconds, it should go to a slower flashing red. If it’s solid red, press the “pair / reset” button again, wait for a bit, and it should start flashing slowly.

Re-open the Harmony App on your phone and select “Setup hub”. Proceed like you’re setting up a brand new hub, but when prompted to setup a new account – select login instead to login to your account.

Next you should get the option to restore your previous settings or start fresh. Select restore and all of your previous activities / devices should be restored.

Key things that took some figuring out for me was how to get re-connected to the hub to set it up after the factory reset. It seems just removing/installing it and telling it to setup a new hub wouldn’t allow it to be found for me because it was looking on my network – I had to completely clear the app out so that it forced me to be logged out. Then it would go through the setup of my wifi and other settings for the hub, which made it discoverable again.