I will find two turtles on a brand new beach id never been to before, feed each sea grass, both enter love mode, get near each other, kiss, xp orbs drop, then nothing...
neither turtle digs and neither turtle lays eggs. sometimes they will want to get back into the water, but still never come lay eggs. then only 1 will be able to be fed again and enter love mode while the rest  will never eat again and thus never breed again. sometimes bred turtle will become inanimate. hitting them makes it move for a short while.
i was able to finally get 2 eggs laid (very early in testing). those eggs hatched like normal but still. breeding the new turtles does not produce eggs and renders them unusable again.