When a user shares their task list with you, confirm you have the proper permissions. All tasks will show on the right hand side by default. This is a common service for all Exchange accounts.

Based off your screen shot, it shows the one listed task. If you have no active tasks, they will not show in the list view. try testing this by creating a simple 'Test" and Test 1" tasks. Put one task in your task list and one in the shared task list.

Hope this helps.