Complex sentence: Clicking on potential hazards is acceptable, but the scoring window only opens if that hazard develops, thus examinees have to remember to react if the status of a hazard changes, and not just when the potential hazard is first spotted.
Split into simpler sentences: Clicking on potential hazards is acceptable, but the scoring window only opens if that hazard develops. Therefore, examinees have to remember to react if the status of a hazard changes, and not just when the potential hazard is first spotted.