Is there an acceleration or drafting bug going downhill

This morning, on a group ride on flatlands loop, I was ahead of the pack coming to the second village. The pack was doing steady 2.0W/kg. So I soft-pedaled through the village, with the pack catching up with me just at the start of the 1.5 mile descent to the arch. Expected to have to pedal a bit harder to accelerate to the pack speed. But, found having to go about 3.5W/kg the whole 1.5 miles to the arch in order to stay in the middle of the back. After the arch, where it flattens out, I could immediately slow down to 2W/kg to stay in the pack. Seems either the acceleration or drafting doesn’t quite work right going downhill. Any idea.