Answer: Sleeper effect
Explanation:
Sleeper effect is the impact in which delayed increase in persuasion effect is observed with respect to the message in communication. Immediate impact not seen in such case rather after some amount of time, message receiver tends to change attitude towards low credibility message.
According to the question, situation in which high credibility message loses its persuasion or low-credibility message attains more person over certain period of time is due to sleeper effect.