User not found when trying to set assignee

[Vasilisa_Troegubova]

Previosly it was ok, but from yesterday I can't choose one of my Jira users as assignee when creating a task (like if the user does not exist). Checked user management and the user is active and it's all fine. 
Noone from the team can assign issues to this user, and the user himself can.

[Avinash Bhagawati {Appfire}]

Hi @Vasilisa_Troegubova ,

Can you please check Assignable Issue permission in permission scheme associated with project.

Thanks,

Avinash