The elevation look ahead was supposed to be fixed ( back in v1.92 ) and show you elevation on your route only.
Today I rode Zwift Unlocked Long on London Calling, and as we were came out of tunnel towards the Box Hill turnoff, the elevation graph was definitely showing the Box Hill elevation, not the elevation straight ahead that the route was going to take.
Once we got almost to the actual Box Hill turnoff, the elevation profile switched to the straight ahead elevation.