Here's my .02
I would replace the rod bolts and recondition the rods. Also, would clean out the motor and and all
oil passages in the motor and head and any nocks and crannies.
If your running a
oil cooler clean that out as well.
Things happen!!!!!
It could have been contamination, clearances, or torque pressure.
I am sure this time around you will have better success. Retorque your bolts 3 times and dont take anything for granted.
Even the best of us make mistakes. At least your engine builder owned the problem.