It stopped when I uninstalled NCrunch. When I can, I'll reinstall and see if it returns. If it returns, I'll try to answer your questions.
Basically, when I opened a cshtml file, the file would open but there would be no syntax highlighting. I could CAREFULLY click in the file and maybe change a word or two, but it was very unstable. If I used a mouse and selected a block of text or did too much jumping around in the text, Visual Studio would crash.
Details of the crash:
Problem Event Name: CLR20r3
Problem Signature 01: devenv.exe
Problem Signature 02: 12.0.21005.1
Problem Signature 03: 524fcb34
Problem Signature 04: Microsoft.VisualStudio.Html.Package
Problem Signature 05: 12.0.40918.0
Problem Signature 06: 523a30e4
Problem Signature 07: d0
Problem Signature 08: 0
Problem Signature 09: System.NullReferenceException
OS Version: 6.1.7601.2.1.0.256.48
Locale ID: 1033
Additional Information 1: 0a9e
Additional Information 2: 0a9e372d3b4ad19135b953a78882e789
Additional Information 3: 0a9e
Additional Information 4: 0a9e372d3b4ad19135b953a78882e789