Forza Motorsport Race Delay

When playing Forza Motorsport (FM) via PC on my DD+, my vehicle fails to move at the start of races. When the start countdown ends and my car doesn't start and the vehicles are passing me by, my vehicle only moves when bumped from behind by another vehicle. This only happens on FM and only when playing via wheel/DD+ (works fine on controller). Several troubleshooting tips from FM have failed to resolve. I've even tried resetting my DD+. Any advice?