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. 

Issues Fixed in 15.9.23

• Fixed C++ compiler bug for proper folding of inline variable dynamic initializers. Ported from the VS 2019 16.0 release.
• Security improvements in vctip.exe.
• A change to enable Enterprise IT administrators and deployment engineers to configure tools like Microsoft Update client & SCCM to determine applicability of VS2017 updates hosted on Microsoft Update Catalog & WSUS.

Security Advisory Notices

• .NET Core Denial of Service Vulnerability 

This release include a set of bug fixes reported against TypeScript 2.8.1. For the complete list of fixed issues, check out the fixed issues query for TypeScript 2.8.3.

npm install -g typescript

A WYSIWYG editor developed by the folks at Basecamp and creators of Ruby on Rails. 1.0 has just dropped and introduces support for image galleries. 

• Fixed issue when using HotRestart to deploy iOS application.
• Fixed and issue where Xamarin.iOS fails to build with MessagingRemoteException.
• Fixed an issue which would place constant-initialized static local 'const' variables in 'inline' functions which were previously dynamically-initialized in the read-only data segment. This can cause compatibility issues when linking against OBJs compiled with older toolsets.
• Fixed a build error in Xamarin.Android projects that could be encountered when Android layout files contain certain characters.
• Fixed an issue with .resx localization at runtime for Xamarin.Android applications.
• C++ IntelliSense vcpkgsrv.exe frequently crashes with set_parent_scope_on_push.
• Fixed WMI Provider component installation failure.
• Fixed a crash in some cases when displaying the Quick Info tooltip for C++ code.
• Fixed a crash when closing Visual Studio.
• Adds Xcode 11.5 SDK support
• Removes abstract modifier to BGTask

• VS2019 Preview 4 broke conditional compilation symbols in C#
• API has been deprecated
• Android debugging not working in latest release 16.4 "Debuggee returned error code INVALID_ARGUMENT"
• Fixed a frequent UI delay that can occur while using the editor.
• Fixed a crash when an attribute constructor is decorated with itself and Nullable Reference Types is enabled while using C#.
• Fixed an issue that resulted in Visual Studio failing to start or crashing on C# solution load on certain Virtual Machine setups.
• Fixed a bug where user defined conditional compliation symbols are lost when the build properties page is reopened. 

Issues Fixed in 15.9.16

• Assembly does not match code for function
• System.InvalidProgramException: Common Language Runtime detected an invalid program. when instrumenting x64 projects
• Cross-EH mode inlining of noexcept code produces unexpected behavior
• Corrected issue with HTML Help Workshop failing to repair.

Security Advisory Notices

• Diagnostics Hub Standard Collector Service Elevation of Privilege Vulnerability
• Denial of Service Vulnerability in .NET Core

Uses 9% fewer CPU cycles, fixes a long standard LEFT JOIN bug, adds experimental support for PRAGMA functions, has faster LIKE and GLOB matching when using multiple wildcards, and more.