After upgrading to v1.2.3, I got an error when creating a new customer account. This only happens if I assign a group to a new user (Customer) during account creation, error does not seem to occur when I did not assign group to a new user. And there are no problems with Admin and Agent account creation.
Then if I try to click the Create Account button again, it shows duplicate key error. I can confirm that after closing the New Account menu and refreshing the page, the new user has already created.
Before upgrading, I was using v1.1.11 and never had this problem before. Also, I tried v1.2.4 and it shows the same behavior.