A Felt AR3 with a manufacturing defect in the head tube. I'm happy to say that manufacturing faults are a lot less common nowadays due to huge improvements in moulding technology.
This particular fault is a wrinkle in the carbon lay-up. During moulding, the carbon has moved out of place, folded over on itself, and creased. The carbon then cures and locks the wrinkle in place. If the fibres aren't running in the correct orientation then they can't take the intended load. You can see how the faint crack on the surface layer marries up to the shape of the fault underneath. The fault was traced out completely until only good quality carbon remained, which is the basis for a safe repair to be carried out. The customer opted to leave the repair in raw carbon to save the cost of restoring the paintwork, and we finished it with a UV protective clear coat.