By default, API Gateway doesn't open port 7443.
If you want to use port 7443, you must configure "Manage Listens Ports".
Menu -> Tasks -> Transports -> Manage Listens Ports.
Also, if you open port 7443 in "Manage Listens Ports", the above matter doesn't happen.
It seems there is the reason in your WEB environment.
If you want help, you can contact to CA support.