On my Mac I have a Single Actions project with 6 task. When I look at the project 2 of the tasks are not showing their deferred and due dates whereas 4 of them are.
If I hover the cursor over the 2 the deferred and due dates appear then disappear when I move the cursor.
The only difference between the 2 and the 4 is that the 2 are overdue but I cannot work out why this should make any difference.
Are you using a custom theme? Is it possible that the default appearance for overdue date/times has been changed to something that makes them invisible?
The above is just a guess; I’d recommend getting in touch with our support humans for further troubleshooting.