Wedding Photo

Welcome!
Looks like the camera tried to get focus on the dress and although you have a confirmation it didn't get focus. Maybe not enough contrast in the white dress. Were the rings your subject, if so I would have used single point focus, camera can't always decide what you want for the subject.

Curious why are you using shutter priority as opposed to aperture priority with flash, the flash tends to freeze motion and will allow the shutter speed to drop to the minimum set shutter speed if required?