Currently if dnd in any depth is enabled (order_branch & order_branch_free), the dragged element can only be added as a child to a task if the task has currently no children or is not closed.
But it is not possible to drop a task into a closed task which already has children.
But it is not possible to drop a task into a closed task which already has children.
allow to drop as child of currently closed task which already has children
We are aware of the issue that there is no way to reorder a task to a parent task that is collapsed. The dev team will fix that issue in the future, but I cannot give you any ETA.