Looks like the buses are going to the Cambie as their N/S route between the detour instead of Ash.
https://www.translink.ca/schedules-and-maps/route/9/direction/1/map?pageSize=5
It's more clear with no cars on it but the centre lane is just for north bound buses as a priority lane to the 8th Avenue intersection and take a right?
https://trafficcams.vancouver.ca/cambieBroadway.htm
EDIT: Dedicated left hand turn lane for buses onto Cambie south.