Hi Alexij, I'm really glad my post has helped other people. I'm rather curious how long will your PFC and rectifier repairs last. Over the years, I've repaired several different SMPS for consumer electronics, but usually they didn't survive for long. For example, I successfully replaced semiconductors for the main voltages, but a few months later, something else failed (standby voltage supply or filtering capacitors, for example). Consumer stuff is simply designed for low cost, not for longevity. On the other hand, YM-3591AAR are server PSUs, so maybe they won't suffer from this.
Anyway, about your questions:
1. Thanks!
2. I believe NDF stands for No Defect Found. This may cover situations when PSUs showed faults in actual disk arrays (due to heat, vibrations, etc.) but the faults didn't appear when they tested the returned PSUs in 3Y factory.
3. Like I wrote in the original post, I think the resistor faults were caused by white putty on some parts of the PSU. Or maybe the resistors were from a bad production batch. That would explain why 2 resistors caused so large percentage of faults. But yes, your vibrating cable hypothesis may be true, too.