I had a big block come apart on the dyno years ago. It had good oil pressure when it spun a rod bearing. We never figured it out exactly but part of the problem in my case might have been poor oil volume. Pressure was high but volume might have been too low. The other issue in my case was tight clearances and heavy oil. I used some 20/50w which might have contributed to the problem. I was also using a fairly inexpensive connecting rod which might have been part of the problem. Hard to say when just one fails. Could be something about that particular rod or it could be something about the oiling to that one rod.