Typically, there is an area that could be open. A crown fits 360 degrees, so the margin could be open at some point around the crown. Double check the contacts to make sure the crown isn't hung up on the contact. Also, check gingiva to make sure they aren't in the way. A bitewing will be accurate while a PA may not be. How are you determining that the margin is not open clinically unless you have direct access to the margins like a lone standing tooth?