After some more messing around it seems like the C# by Microsoft extension was causing the issue.
Reading the extension i saw this:

How to use OmniSharp?

If you don’t want to take advantage of the great Language Server features, you can revert back to using OmniSharp by going to the Extension settings and setting dotnet.server.useOmnisharp to true. Next, uninstall or disable C# Dev Kit. Finally, restart VS Code for this to take effect.

After I did that it no longer caused the vars to be replaced.