Stop using the blades immeadiately. If those are cracks, the blade(s) could come apart explosively. This could be a very dangerous situation.
Is it possible what you see is cracks in a protective coating on the blades?
If not, I would take the blades back to where you bought them and demand an explanation/replacement.
As to the cause, it could be a manufacturing defect with incorrect heat treat or material or ?
Excessive speed or heat might be the cause, but you would know if you are abusing the blades in some manner.