This sounds a lot like a religious cult whose “end times” didn’t happen on schedule, so they reschedule it to keep their followers fired up.
"Disconfirmed expectancy is a psychological term for what is commonly known as a failed prophecy. According to the American social psychologist Leon Festinger's theory of cognitive dissonance, disconfirmed expectancies create a state of psychological discomfort because the outcome contradicts expectancy. Upon recognizing the falsification of an expected event an individual will experience the competing cognitions, "I believe [X]," and, "I observed [Y]." The individual must either discard the now disconfirmed belief or justify why it has not actually been disconfirmed".
Good comparison — they are climate Millerites.