Typically I see that when citrus fruits are not at their freshest.
Have you been having cold dry winds? That might be drying out the inside of the fruits.
Also it is known that Changsha doesn't really have the highest fruit quality, but I don't know if that translates into what you are seeing here.
This variety might be more vulnerable to this phenomena of inner drying out, that is a possibility.
Maybe if you've already been having freezes and the fruits have been hanging on the tree too long.