I believe there is an underlying design issue in your system/controller design. The change in Po * Kp following a switch event can exceed the other comparator threshold, causing the switch state to toggle. There is no limitation on the switching frequency in the circuit, so zooming in on the comparator output when the comparator inputs cross each other clearly shows this issue.
One can implement a comparator with hysteresis or reduce the PI gains (e.g. Kp=1), but neither of these really fixes the underlying issue in my opinion.
Is there supposed to be a minimum on-time, fixed switching frequency, or something similar for this circuit?