Quite often, when a new user has a question that is migrated to another site, the user does not have an account on the target site. Unfortunately, because users are only notified about the migration and are not reminded to create or associate accounts for the target site, they may fail to create or associate accounts on the target site. It would be a good idea to give such a reminder, so that they know how to regain ownership of the question and be able to respond to answers and comments.
This is related to Migration to a site where I have no account is a very bad user experience, but the linked question only addresses the account association bonus, and without the user knowing that account creation/association is needed on the target site.
I've read other questions like How to handle a "new user" migration situation? as well, only to find that they do not involve any automated means of notifying the user to create/associate accounts upon migration. Manual notification by normal users becomes impossible in most cases except by ♦moderators because the question gets locked on the source site, so it would really be a good idea to modify the existing migration notice to say something like:
Your question … was migrated to site – remember to create an account there and associate it with your other Stack Exchange accounts. Learn more