These are the customer-reported issues addressed in 15.9.4:

• Visual Studio 15.9 duplicate loads open files on solution reload.
• All users can now connect to on-premise TFS servers through Team Explorer.
• Visual Studio 15.8.3 no longer expands metadata in ItemDefinitionGroup for project-defined items during GUI builds (worked in Visual Studio 15.8.2).
• Visual Studio has multiple tabs for the same file.
• System.ArgumentException: The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG)).
• LNK4099 PDB not found.
• Asset Catalog empty.
• /analyze fails for C++ code using /ZW.
• C++ compiler code optimization bug.
• Xamarin.iOS can't select image asset for Image View.
• iOS projects referencing a shared project containing image assets in an asset catalog fail to load on windows.
• Image not populating on iOS splashscreen in VS 15.8.6.
• Possible bad codegen on union/bitfield assignment in VS2017 15.8.
• Fix C# UWP Store 1201 Submission Issue.
• Fix C# UWP package creation error APPX1101: Payload contains two or more files with the same destination path 'System.Runtime.CompilerServices.Unsafe.dll'.
• Error MT2002: Failed to resolve 'System.Runtime.CompilerServices.AsyncValueTaskMethodBuilder' reference from 'System.Threading.Tasks.Extensions...'" when building a Xamarin.iOS project.
• Redirecting to a relative url doesn't work when using AndroidClientHandler.
• Debug information for typedefs of unnamed enums compiled with the C compiler is now restored.
• The spectre-mitigated x86 version of delayimp.lib is now built with /Qspectre mitigations enabled.
• Changes were made to how Asset Catalogs in Xamarin.iOS projects are loaded in order to reduce solution load time.
• We have updated Xamarin.Forms templates to use the latest version.
• We have fixed an issue with ASP.NET Core Web Applications being debugged through Kestrel that would show the error message "Unable to configure HTTPS endpoint. No server certificate was specified...".
• Enabling the AppInsights site extension in App Service from Visual Studio now happens through the use of specific Application Settings.

Security Advisory Notices

• An elevation of privilege vulnerability exists when the Diagnostics Hub Standard Collector Service improperly handles certain file operations.