Can't load projects with Visual Studio 2019 16.6.0; error : Value cannot be null.

I have been using VS2019 for some time without issues. After updating VS to the 16.6.0 version when opening the solution of my project I get the following error:

C:\Unity Projects\MyProject\Assembly-CSharp.csproj : error : Value cannot be null.
Parameter name: value

I get this error for each project file of the solution. All projects are unloaded and manually reloading produces the same error.
I can open the solution with VS2017 without issues. I tried repairing my VS2019 installation as well as re-installing or even using the 16.7 preview of VS. Anybody else encounter the same problem after updating Visual Studio?

 

Yeah, seeing this too. Did you ever find a solution? I've tried the same stuff. What a ...useful... error message.

I think the XML in the .csproj has gotten corrupted. I compared the .csproj against a new project's that works using Beyond Compare. The ItemGroup designations changed. In the working file all of the Reference tags are in their own ItemGroup, and all the compilation files (*.cs) are in their own ItemGroup. In the broken file, these are intermixed randomly. I fixed this, and I can open the property sheet now. However I'm still not able to attach to Unity. Working through that one now...

 

Figured it out. This bit was missing from the project for some reason. Not sure if this GUID will always been relevant, but placing this in the XML within the <Project> got it to start debugging for me again:

Code (XML):

1.   <PropertyGroup>
2.     <ProjectTypeGuids>{E097FAD1-6243-4DAD-9C02-E9B9EFC3FFC1};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
3.     <UnityProjectGenerator>Package</UnityProjectGenerator>
4.     <UnityProjectType>Game:1</UnityProjectType>
5.     <UnityBuildTarget>StandaloneWindows:5</UnityBuildTarget>
6.     <UnityVersion>2020.1.4f1</UnityVersion>
7.   </PropertyGroup>