The fact that the cracks are originating from the metal support plate leads me to believe there is something suspicious about the stress distribution design in this region of the blade. Unless there were issues with the manufacturing of the laminates (i.e., contamination between layers, poor curing temperature control, nonuniform heat press, etc.), consider performing a FEA on the blade composite structure and verify no cyclic stress limits are exceeded, especially at the metal-fiberglass junction.
