What is the reason a sub task is not linked to the upper level?
This should be veryf helpfull
Which of our apps are you referring to, mobile, browser extension, website, desktop? On all of these platforms a sub-task is always attached to the parent task.
On some views, such as Today or 7 Days, it can seem like they are not linked, because if they all have due dates for Today, they will show up as their own task to complete. If you view these tasks within their own project, you will see they are indeed linked together.