Fanning Mistake

Hey eveyone. Recently just started having a weird thing happen to me while fanning or using the s method with trad. Every so often I’ll notice these random maybe 1 inch by 1 inch missed spots right in the middle of the window. Is this the rubber skipping or me lifting up the squeegee when I make a turn? More of a recent development and it’s causing me to have to detail so many windows with a dry rag, slowing me way down. Thanks!