Fig2 ,Page 7 of the attached DER-275 document shows a 3n3 capacitor (C14) across the lower feedback divider resistor of an SMPS.
(Page 9 of this document says that this capacitor is there because of noise getting injected into the TL431 reference pin.)

Do you agree that this capacitor should not be there?
The way to address that noise would be to use a far smaller value capacitor. C14, at 3n3, would need to be included into the error amplifier small signal transfer function.