It’s come to my notice that there is a problem for travelcard holders on Oyster with the gates for platforms 2-5 at Paddington. If you travel in from the West using a ticket to the boundary of the highest zone on your travelcard, then touch out using your travelcard at those gates, you will be charged a fare from Heathrow using Heathrow Express. The same will also apply in reverse. That’s a £22/£25 interest free loan to TfL until the help desk issues a refund.
TfL are aware of the issue and I’m waiting for a response.