For the latest documentation on Visual Studio 2017, see Visual Studio 2017 Documentation.
Problems with IntelliSense code snippets are typically caused by two problems: a corrupt snippet file or bad content in the snippet file.
The XML in the snippet file may be corrupt. The XML Editor in Visual Studio can locate problems in the XML structure.
The snippet file may not conform to the snippet schema. The XML Editor in Visual Studio can locate problems in the XML structure.
You may be missing a project reference. Examine the documentation about the snippet. If the reference is not found on the computer, you will need to install it. Inserting a snippet should add to the project any references needed. If the snippet is missing the reference information, that can be reported to the snippet creator as an error.
A variable may be undefined. Undefined variables in a snippet should be highlighted. If not, that can be reported to the snippet creator as an error.