same exact issue, I followed the guide EXACTLY. I check the firmware and everything, perhaps signing in with my account is what's messing it up? I even tried older versions of the app and still nothing.
SOLUTION! turns out my Flex 2 tweak was just plain bad, I downloaded Flex 3 and it worked like a charms. Another thing I checked is if you download any other patches for chegg make sure they're not enabled. (I know Flex was bad because the patches did not affect another App that I had patched.) Redownload flex then try again, Make sure it's 2.8.1!
Thanks @Doesthismatter for helping a homie out, This method works 4-25-17, just tested it myself.