I changed my Smartthings Hub today because of a problem.
Then I installed all my devices and apps. It was a real difficult task.
Now I want to make the change on Amazon Alexa app but after I login through Alexa to ST and authorize it for several devices, Alexa app does not discover my ST devices.
You may need to talk to SmartThings support. Most likely the second hub was added as a second location, assuming you’re using the same email address, and echo can only find the original SmartThings location on your account.