Media Protection acting WEIRD!

The protected files on this membership site are accessible to the public. I have one membership level in the site and certain PDF files are protected and supposed to be accessible only by members of that specific membership. But it is not working that way, some files seem to be protected and some not. And their behavior changes from time to time. We assumed SG cache was messing up which we disabled to check if it was the culprit, but it wasn't. We did a conflict test which still didn't help, their behavior kept changing, by changing we mean, suppose a file is protected at this moment but after some time it becomes accessible. Some protected files are not accessible even after logging in as a member, they still stay protected from the members who are supposed to access the files. Debug.log wasn't generated and we've also tried with a default htaccess file. Nothing worked. Any help is appreciated. Thanks!