Line bore, or maybe a warping line bore after assembly. I am not familiar with the bottom end of this engine but I'm thinking there is a whole lot of aluminum. I don't love any marriage of Aluminum to Steel or cast iron. Aluminum has an expansion rate when heated 10x that of cast iron maybe susceptible to bore warp among a lot of other things.Then why on the couple of engine tear downs I've seem do they show signs of line bore issues? Line bore issues can and usually do cause spun bearings aka a common issue on these. Also use to have issues with a certain rod failing which was blamed on an assembly line torque issue. That issue supposedly got fixed and is way less common now. While I do think the bearings are weak and need replaced with a tri metal design I dont think thats the root cause of most failures.