Hello, you are not alone. Same issue to all that had domains in Google and now our "friends" of Squarespace do nothing to solve this. I have tried login from incognito mode from a different web browser, log out and log in in the same minute and even clear all the "config" placed after the migration from Google. Now I'm able to add aliases from 2 of my 3 domains hosted in Squarespace. And yes, seems like the support of Squarespace does not matter what happen to his customers. We are alone here. Very sad for a "world class" service.
