It does appear that these issues stem from design or faulty materials. However, Boeing employees are really irate over the company having a facility in South Carolina. I wonder if there might be some union sabotage occurring. Not saying that is the case, just a thought. I just know how ticked the workers were.
Back in the 70's to early 80's, Harley Davidson motorcycles were unreliable due in large part to union sabotage. After AMF bought Harley, worker dissatisfaction increased, and product quality suffered. Nuts and bolts were found in crankcases, parts were installed backwards, parts were machined to incorrect tolerances.
Due to lessons from the past, any speculation that some of this may be happening? If so, its a real bad situation when your dealing with airplanes ( motorcycles, too, for that matter).