Using the rear connector reduces your operating time by about 7%.? In any case, that relay is known to develop dirty contacts and fail intermittently.? You might try cycling the relay F-R-F-R to see if the contacts making and breaking helps the contact, OR try using the front connector and see if your problem changes.
The antenna front/rear relay is one of the known problems of the FT-817.? It should have been a latching relay to preserve battery life.? But the FT-817 is a 23 year old design that has sold well over ?-million radios.? Show me another ham radio that has done this well.