From what I know Photo, sometimes Fillet is really fickle around the seams in things, especially when they cross with other things you are trying to fillet.
Try to rotate that sphere around to get that seam line in a different position.

But also, I've had disappearing icons and a messed up UI due to whenever my Internet Explorer crashes or has been way out of date.
So on your Mac system, make sure that M$ IE is updated.
But Michael will have better knowledge for ya.

Good luck.