Missing tasks in users' timesheets - why ?

One of our users can't see some tasks assigned to him : 

- He can see projects where he has been assigned time, 

- He can't see tasks where he has been assigned 

- The timesheet does not display the new tasks. 

- The timesheet displays some old tasks 

I already changed the Assigned owner and the Booking type for this user, but with no effect. 

Please help, i'm going crazy 😐 

Laurent.