Your entitlement server has to report back to us the product IDs that the user is entitled to. If your entitlement server isn't doing that then they won't get access.
This is definitely an issue with your entitlement server setup. What entitlement server are you using and who set it up? You should check with them to see how you should be associating a user's email address with product IDs for entitlement.
This sounds like an issue with the entitlement server setup. Does the entitlement server give the user access to this collection (and by extension all articles within that collection) when the user signs in?
If you need help, you might want to call support about this issue. Support information is listed in the DPS Portal when you sign in using a Master Admin account.