2017 ram 2500 broken manifold bolts

I agree that the failures are mechanical/thermal fatigue related, but I don't see any potential for a shear component. The major forces are acting on the z-axis of the bolt, not shear in the x-y axes. It's a moot point really. The fastening system isn't reliable enough and either didn't go through accelerated life testing, or the results were not properly acted upon. Just like all of us, these companies make their choices and take their chances.