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I deleted the user, now I'm trying to login again. I noticed two things:
1) when I delete a user, using the users interface, it does not refresh and says no messages (I think it is a frontend issue but because of it I cannot know when a user is really deleted).
2) Now that I waited for a longer time to login (after deletion) I can login with that user so it correctly creates it.
It seems to be a timing problem (synchronization), in production we cannot enstablish that time (and the number of retries that a user can do for the login).