A recent update changed the behaviour of duplicating a Task that has Custom Fields. Previously, the Custom Field checkbox on the duplication modal meant that you intended to duplicate the stored values from the previous task to the new duplicate task. The new behaviour forces a Task with Custom Fields to be enabled, not optional, stating "This task has required Custom Fields that must be included." This is not desirable, as you would now have to manually clear the Custom Field data on your new Task. Duplicating a Task with Custom Fields (at least within the same List / Space) would always duplicate the presence of the field, because the Custom Field is never Task specific, it comes from higher up. If you duplicate a Task with Custom Fields targeting a different List / Space with a different CF configuration, you get the conflict resolution modal, so there's no reason to force the user to duplicate the VALUES in those fields at this moment. Consider renaming this checkbox to Custom Field Values if it needs clarity, and do not make it a mandatory option.