Oct 12, 2025

No, none of that. If it includes a double spend of an ancestor (i.e. in its branch) or if it spends an output that is not in its ancestry. That's the only way it becomes "unconfirmable" (another terminal state) once it's been validated. Though this can also be caused by one of its ancestors becoming unconfirmable (which can be caused by the above, or by invalidity). Unconfirmability propagates to all descendant blocks.