I have tried using different iphones & ipads (with latest iOS ) login to my QlikSense server hub, all of them prompt the same error message"An error occurred Connection to the Qlik Sense engine failed for unspecified reasons. Refresh your browser or contact your system administrator."
This error occurs when i access the hub through internet on iphones or ipad.
I have already whitelisted my server IP address and machine name in QMC.
If the test confirmes that the WebSocket protocol is not allowed and you have properly configured the host white list then I would look into any network equipment between your IOS device and the Qlik Sense server (Firewall, reverse proxy, vpn) and see if any of these is blocking the websocket protocol.
Hope this helps!
Bastien Laugiero If a post helps to resolve your issue, please mark the appropriate replies as CORRECT.