<p>In order to probe into the potential to improve students’ fluency by using formulaic sequences (FSs), many studies explored the relationship between FSs and oral fluency. However, their findings are sometimes conflicting, without adequate explanations. Yu’s (Front Psychol 13:1012225, 2022) study suggested the reason to be that processing advantages of FSs might be neutralized or weakened. This follow-up study takes the structural type into consideration, and explores why FSs sometimes lose processing advantages in oral fluency, using a combination of quantitative and qualitative methods to investigate 120 spoken narratives. Results revealed that despite the small number of fixed FSs, they still mattered more to speakers’ speed and breakdown fluency, compared with open-ended FSs. Besides, only the proportion of fixed FSs was positively related to speed, and only the variety of open-ended FSs was negatively related to repairing. The findings suggest that open-ended FSs sometimes fail to promote speed or breakdown fluency, and corrected or reused open-ended FSs could even impair repair fluency. Theoretical and pedagogical implications have been provided accordingly.</p>