I am having an issue with an off flavor on my IPA only when kegging with force carbonation. The same beer tastes great when bottled with carbonation drops. I have done a split batch to test it out. The lines are clean, the temperature is about 34-36 in the keezer, and the CO2 is done per the chart. I close transfer from a stainless steel conical and fill the keg with starsan then push it out with co2. I do not see anyway oxygen should be an issue. My cleanliness is probably overkill. The beer has a harsh bitter aftertaste. I cannot seem to figure out what my issue is. Any assistance that could be provided would be greatly appreciated. I am extremely frustrated right now.