Email address should be define in FND_USER and PER_PEOPLE_F tables for the User who is not getting workflow.
1) Check for Table : FND_USER
End_date should be null for the user who is not getting Workflow.
2) Check For Table: WF_LOCAL_ROLES
Expiration_date should be null for the user who is not getting Workflow.
3) Run Request : Workflow Directory Services User/Role Validation.
Schedule request periodically as per below parameter.
