I have the same problem. I am flying to JFK. I received an API email from BA. My passport etc is already there but I need to add hotel address etc and my Global Entry Known Traveller Number. This was always possible previously, but now when I can actually manage to get to the add passenger information page (without it saying 'we're experiencing technical difficulties') only passport details are available. There is no way to scroll down to add anything beyond the already-saved passport details. Kind of a problem for flights to the US where some of this needs to be added at least 72 hours in advance.