1050 [CORS] Preflight request failed when there's an HttpOptions route attribute
This is caused by the presense of the route data in the request used for selecting the EnableCorsAttribute on the action. The route data contains information about the preflight request and not the actual request therefore failing to find the expected EnableCorsAttribute.
The fix is to exclude the route data so that it's regenerated for the request used for selecting the EnableCorsAttribute.