I have a Fattwin F627R3-R72B+. One of the nodes has no power. If I swap the nodes, the problem stays in the same slot, not the same node. So it seems it is a backplane issue. There are 2 backplanes: BPN-SAS-F424-A2 and BPN-SAS-F424-A6. Which one is related to power?
Both of the backplanes you mentioned are hard drives backplanes. They are not power backplane.
The power backplane is located inside the chassis and the part number is BPN-PDB-F418. Since it is hard to replace this board by yourself, it is recommended that you RMA the enclosure (you keep nodes but only swap the enclosure) if needed.