Using nested Scaffolds can cause unexpected behaviors that rush new issues into this repository,
to prevent further issue reports related, I suggest an assertion in the Scaffold Class just for Debug Mode:

assert(() {
  assert(context.ancestorWidgetOfExactType(Scaffold) == null);
});

These are some of the issues:

• keyboard - padding added to the Scrollable #23051
• Keyboard overlap all widget with nested Scaffold #20289
• Double stacked material scaffolds shouldn't double resizeToAvoidBottomPadding #12084
• bottom overflow issue, when using textfields inside tabbarview #20295