Thanks - I had to wait for a bit for the http error log to appear.
Microsoft.ReportingServices.Portal.WebHost!reportserverwebapp!d6!10/20/2017-09:07:24:: e ERROR: [mgggtq10]: OData exception occurred: System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it {SSRS IP}:443
Looks to be a HTTP SSL issue or firewall ACL issue. This is enough for me to work with my networking/server friends. Thanks for replying.