When editing a process and the user needs to drag a Task to an Activity that is not on the visible screen, the screen should automatically scroll when the task is dragged past the top or bottom of the activity list. Right now you have to drop the task close to edge of the list; scroll the screen; drag and drop; scroll; etc.
If you are still not able to scroll while dragging a Task please reach out to our support team, and provide details of your browser as this may be the issue.
Thanks!