Please watch the video: https://www.youtube.com/watch?v=NDXuoL8HwJM
It looks to me like you are creating the user when creating a claims record. So when you create a second claim for the same user, the user is already in the table and can’t be recreated as the email address needs to be unique?
In the claims form, the field for the user could be a connection field to the users table which allows you to look up the user and add it/them to the claim. I have a similiar use and i add my users first and then ceate the case (claim in your case). I guess you could add the user at the time creating the case if they are not already in the table by using a connected record rule. I haven’t tried this so not 100% on it.