Summary

When placing an observer on sales_order_state_change_before, it's not possible to get any data from the actual order object.

Examples

see \Magento\Sales\Model\Service\OrderService->setState():

Current code is:
$this->eventManager->dispatch( 'sales_order_state_change_before', ['order' => $this, 'transport' => $transport] );

Because $this is passed to the observer, and not $order, there's no way to get order data in the observer.

Proposed solution

Change event dispatch either to 'order' => $order, or add 'order_object' to have it backwards compatible.

$this->eventManager->dispatch( 'sales_order_state_change_before', ['order' => $this, 'transport' => $transport, 'order_object' => $order] );