Fan and Mortar Geysers are two geysers in the Upper Geyser Basin in Yellowstone National Park. For the past several decades, they have erupted in concert with one another and are generally talked about together. The records detailing these geysers' known eruptive history shows that they have been infrequent and irregular performers.
Fan and Mortar Geysers can both go more than a year without any eruption
The context says that Fan and Mortar Geysers are infrequent and irregular performers. It does not say whether or not they can go more than one year without any eruption. The computer might have been confused and thought the statement was claiming that they don't erupt at all