Azure Functions Host appears to be looking for dll's that don't exist

I initially hit this https://github.com/dotnet/core/issues/4390 which in turn led me to https://github.com/dotnet/roslyn/issues/42445 because i noticed this only happened in my functions project and not the rest of my stack.

The roslyn guys have suggested "quote" ...

> Microsoft.CodeAnalysis is a metapackage that contains no dlls at all. instead it references all other roslyn packages. It exists as an easy way to take a dependency on a specific version of all roslyn assemblies.
>
> Microsoft.CodeAnalysis.Common is a set of common libraries that all other roslyn packages have a dependency on. It is unlikely you ever need to reference this package directly.
>
> From reading through the issues you posted elsewhere @TehWardy this may be an issue with the Azure Functions and which set of runtimes/dependencies it supports. I would file an issue on https://github.com/Azure/azure-functions-host

... so here I am.
Any help with this would be really appreciated as I have an urgent need to get a deployment through for an important project.