I can't find a user or add him to a team in the "people" section

[Alexandra Grasland]

I can see the user in the administration panel, he is like any other user.

I can't mention him with @, the search engine won't find him.

I cannot add him in any team, or find him

[Alex Koxaras -Relational-]

Hi @Alexandra Grasland 

Are you searching him by name, or by email address?
Has he ever logged in?
Did you try copying his first name, and then paste it after the @ to see if Jira finds him?