This also happens when planes land at KLAS on runway 1L and exit to Sierra and to a lesser degree November. The performance drops markedly if the aircraft is allowed to wait for more than a minute before giving the order to "Taxi to Terminal" when at those exits. As soon as the order is given, the performance plummets and once the autocalculated route is displayed, the performance returns to normal. It makes no difference if I give a route with the Taxi to Terminal. Usually if it's the only aircraft at KLAS, it won't degrade, but most of the time I see this at that exit is when there's 5+ aircraft on the ground.
It seems to be avoidable if I give the order to Taxi to Terminal before they reach the exit. If avoided, it's not nearly as bad.