Hardie plank is pretty tough stuff. I don't think that is random deterioration. I think it's mechanical damage that occurred during the install. It's all at sharp edges where the siding could have gotten easily fractured during handling. It's possible that some of the chips did not immediately break off but were held in place by the fibers in the siding for a long while. Bottomline: I don't think there is anything bad going on with your siding. I have Hardie siding in a different style that is more than 20 years old and it shows no deterioration. I think yours is fine and I don't believe you will see any new issues appearing.