Something wrong with the Harris transmitter. It's back on the Nautel and other mast for now. This is the message on their website:

Service Message: Monday 21st July. Our 648 AM is currently on reduced power on our standby transmitter following thunderstorms and lightning strikes in the Orfordness area on Monday afternoon. Our main transmitter has shutdown with an HV overload and will not restart. We will arrange an engineering team to site shortly.