IntelliSense in Razor files (.cshtml) stopped working

This is what worked for me after IntelliSense suddenly began to bug out and stopped colouring C# code correctly in between the HTML tags in my views:

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Just delete the contents of the folder at %LOCALAPPDATA%\Microsoft\VisualStudio\16.0_<hash>\ComponentModelCache

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As an additional step, you can optionally run the command DevEnv.exe /setup in Developer Command Prompt for VS (as an Administrator) if the above step doesn't resolve the issue.

When intellisense stops working in the razor file, there's a good chance that the issue can be fixed in three steps:

1. Close Visual Studio
2. Delete the solution user options file (<solution-name>.suo)
3. Re-open the solution in Visual Studio.

Other solutions for intellisense options can be found here.