ERG mode with Wattbike. Power jumpy


I’ve just ‘upgraded’ from a Wahoo Kickr to a Wattbike Atom. Doing a workout in ERG mode on the kickr was easy and the wattage was smooth. In the same mode on the Wattbike, the wattage is jumping around all over the place. Any idea why? It’s making the training quite difficult to manage.