I've got this ASP.NET Core site (version 1.1.2 with target .NET Framework 4.6.1) that is hosted on a Windows Server 2008 R2 using the .NET Core Windows Server Hosting bundle. It works fine everywhere, except on Safari (11.0) on macOS (10.11.6) where it intermittently gives the error "Failed to load resource: The network connection was lost.".
This error happens immediately, e.g. when POSTing a form. There is no delay or loading time. It is reproducible on different Macs. It does not happen with other browsers on the same Mac. Safari on the same Mac works fine with other sites (e.g. "old" ASP.NET MVC applications on the same server). So this leads me to the conclusion that it has something to do with the combination of Safari and ASP.NET Core (with IIS/Kestrel reverse proxy) hosted on Windows Server.
Unfortunately I have no idea how to analyze this further, since Safari does not display any detailed error and nothing shows up in the log files on the server (the request is logged with HTTP 200).
Anyone having similar problems or ideas to analyse this further?