Update February 12:
High performance PC builder Falcon Northwest has taken to X to say that it has tested "many" RTX 5090 FE cards, but has been unable to repeat der8auer's findings. Falcon Northwest's thermal images show much more balanced loading on the power cables wires, something confirmed by measuring the currents.
Some observers suggest that the problem may be linked to the number of times a cable has been attached and detached, with der8auer having said that his cable has attached and detached numerous times. Watch this space for an official update from Nvidia.