Another possibility is that the #8 rod got 'trapped'....by #7 rod. #7 rod might be bent, or has been closed & honed in the last re-build & the machining left the rod at angle. The bent #7 forces the #8 rod against the crank cheek. The oil to #8 rod is now unable to exit the brg, quickly overheats, breaks down &...brg failure.
To prevent this happening, I grind 3 oil reliefs in the rod. One at 12 oclock, one at 10 to 2 & one at 10 to ten, these last two in the bolt column. These 3 areas are the strongest part of the rod. I make the relief about 1/4" wide, 0.030" deep. If a rod is now forced against the crank cheek by it's neighbour, the oil can exit & fresh oil can enter the brg.