Source: Upcoming change to the Google Tasks API from Google Cloud
We recently updated Google Tasks to limit the number of nested tasks a user can create (also known as a “subtask”) to be just level. While subtasks are supported, any tasks nested beyond these—like subtasks of subtasks and so on—are no longer available.
Starting August 30, 2019, we will introduce the same structure in the Tasks API. This means that as of this date, tasks that are nested beyond more than one level will no longer be supported. Tasks that are nested beyond one level will automatically be converted to subtasks.
Who is impacted? If you’re a developer with an application that supports multiple levels of subtasks, like apps for project management, note taking or checklists, you may be impacted. This could also include applications that are reliant on the Tasks API.
What should you do? Please check and update your applications accordingly if they support multiple levels of subtasks.
These changes will take effect on August 30, 2019, so you will have close to a year to implement these changes in your application.