Hi, for second issue, that is not a bug
Your pulses are too short that blocked by interrupt filter
you can remove filter, then it will work with your special frequency/duty cycles.
Below is where we added, it needs to be before the pin is assigned to digital.
....
var digitalSignalPin = GpioController.GetDefault().OpenPin(SC20260.Timer.DigitalSignal.Controller2.PB3);
digitalSignalPin.DebounceTimeout = TimeSpan.Zero; // GHI added
var digitalSignal = new DigitalSignal(digitalSignalPin);
var waitForEdge = true;
.....