An upgrade has been performed to version 15.9.3. After this, the App URL is not accessible using the HTTPS protocol. It is however available through the HTTP protocol. The application has been configured to support both HTTP and HTTPS at the same time without switching.
Further, the NSA URL is also available through both these protocols.
All the relevant ports have been checked. They have been determined to be open as required.
The 15.9.3 folder structure that had been obtained after upgrade was rebuilt to resolve the issue.