URL ending with a double slash and percentage number

According to my “Visitor’s Map” plugin log, one of my last visited URLs showed up: https://diabeticssupportsocks.com/choosing-diabetic-support-socks//%22, which directs to a 404 error page rather than https://diabeticssupportsocks.com/choosing-diabetic-support-socks/. I tried to fix it using my redirection plugin, but it had no effect. Any idea why my URL is ending with that and if there is a way to change it? Thanks.