If you have a user who is having difficulty logging in after the GTMA IV release, a likely cause may be that a duplicate record exists in the user database. When the user requests a password reset, it may be resetting the duplicated account rather than the one intended.
In order to know if there is a duplicate, go to the Customer Users page and search on the user's email address. Make sure to enable viewing inactive users. If there's a duplicate, you will see one or more users with the same email address.
See more troubleshooting solutions in the screencast here...
Introduction to GoToMyAccounts Gen IV