I dove in the area right near Kepler City, and it won't let me surface from the dive.
Just to check, are you sure you aren't trying to surface in an unsurfacable location? The lighting is very slight, but you can only surface in places where the lighting is brighter than regular sand tiles. It might be hard to tell, but you should try that.
Yes, I was in a lighted area where it said - The light is brighter here - A pokemon may be able to surface. And then it wouldn't let me surface.