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