Tasklist task 100% complete but milestone shows as overdue

Tasklist task 100% complete but milestone shows as overdue

Hi

I have a tasklist with a milestone associated.  The tasklist has one task.  A team member has updated the task to 100%.  The task shows complete, and the tasklist has no open tasks.  When I go to the milestone screen, I can see this milestone is 100% complete (green bar) but that it shows in the overdue section instead for the completed section.

Please can you help?

Thanks

Cameron