Sportster jerks downhill

Hi together, I’ve been driving for almost 200km ne sportster Iron. If you roll down a steeper mountain with your sportster at approx. 2500 -2800 turns in the second gear and take the gas away then the bike moves as if I were driving over a wavy ground. Now my question is this normal at harley because I’ve never driven a machine with belt drive or do I have to be friendly? Thank you