Are you powering more than two risers from one lane of your PSU?
You should not connect more than two risers to one lane.
SATA: Limited to one per rail.
MOLEX: Limited to two per rail.
6 Pins PCIe: More useful for powering GPUs rather than a Risers.
Thnanks for the clarification, I was not aware that it's best practice to only use one riser per SATA rail.