That is strange. I agree with you with the customers letting you know. I have quite a few regulars (3-4 visits a week) that have my personal number to let me know if they have or see any issues.
My last thought about your issue is kind of a stretch, but I've always worried about the internals of the swipers getting shorted out from water damage. You would have to take the swiper apart (which could void any warranty or mess up any internal seals) to check but like I said, its kind of a stretch.