Ampera aka IGOR
Tesla Model 3 P
My understanding, and could well be wrong, is that the road was open when you first entered the destination into the navigation. At this point, it checks the latest traffic update received and is confirmed as ok to route that way. The closure is then relayed but the car has not received the details yet but may well in the next few minutes and decide to re-route you. When you request the navigation again it checks for traffic information immediately and is notified of the closure and so routes an alternative.