I recently added a new user to Jira. I created some issues and assigned them to the user.
He can see the issues if I send him the direct link to the issues.
However, the team-managed project board does not list the user in the top filter. The user does not appear in among the users listed in the filter options. Moreover, if I open the user profile from People -> NameOfTheUser I see that "There is no work to see here" but I do see the project listed under "Placed they work in".
The user has been already added to the project with Member permission. He can see the issues if he opens the url I sent him. He can even add subtasks or edit the ones already created and assigned to him.