What you are likely to see are high switching losses and poor overall efficiency.
One solution is to re think your magnetics design.
Too many turns on one winding, often a single high voltage secondary, and poor winding technique are usually the cause of a low self resonant frequency.
You need to reduce the ac voltage gradients between adjacent turns, and hence the inter turn capacitance by careful design.
One trick is to break up a high voltage secondary into several individual sections, each with its own rectifier and filter capacitor, and series connect the dc outputs.
Perhaps one complete full layer per high voltage section.
Several single full layers placed one top of the other can have a high dc voltage between layers, but zero ac voltage between individual turns to the layer above, and the layer below.