An impediment that prevents a legal effect from arising differs from one that interrupts an effect already established. The temporal and legal location of the impediment matters.
Prevention of formation of a cause and prevention of its completion concern the causal process. Prevention of the ruling’s commencement and prevention of its continuation concern the effect at different stages.
Therefore saying simply “there is an impediment” is incomplete. Specify whether the cause never formed, failed to mature, the ruling never commenced, or an ongoing effect ceased. That diagnosis determines how the example should be analyzed.