I have had this problem with Chase too, about a year ago. I think it’s just them. I was in Nordstrom and made purchases from two different departments in the store. The first went through and the second was denied. I got the same story from them about fraud and they were just trying to protect me and whatnot, but it was very annoying and I cancelled the card (for this reason and because they kept sending me “checks” even though I had asked them repeatedly, in writing and over the phone, to not send the checks). I have not had this problem from any other credit card company.