Did you customize anything in the theme? I think revert back to the theme first stage can diagnosis the problem. Also I have noticed bbpress or buddypress are causing this redirect issue. I have work out on google and get some knowledge that bbpress can redirect a page. I developer who worked in the site can know well.
You can disable all your plugins except User Frontend and switch to a default theme of WordPress like- Twenty Twelve, Twenty Thirteen, Twenty Fourteen and let me know the results.