I think maybe it is because the status change only happens after the next step begins, which means the bg check usually is the last step in WH, and the status won't change until the others office like calgery or vancouver take over our case.
For now, as I know, calgery process cases faster than the other, so if you are lucky, your case maybe sent to calgery, once they start processing, the status would change from that moment. If not, your case maybe need to wait the other offices to take over.