Omnisharp breaks after last update

[nxfs]

Issue Description

After updating the Omnisharp to v1.37, it fails to start.
The first problem is that this error appears:

[fail]: OmniSharp.MSBuild.ProjectLoader
        The reference assemblies for .NETFramework,Version=v4.7 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks

I figured that by overriding the framework it goes away:

export FrameworkPathOverride=/usr/lib/mono/4.7-api
code

However in this configuration Omnisharp fails to recognize classes defined in nuget pacakges

I realize I can reproduce the problem outside of VSCode:

dotnet msbuild  project.csproj

scenes/city/tgf/SplineTransform.cs(1,7): error CS0246: The type or namespace name 'Extreme' could not be found (are you missing a using directive or an assembly reference?)
...

However if I build with the mono msbuild it works fine.
The difference is as follows:

msbuild -version
Microsoft (R) Build Engine version 16.6.0 for Mono
Copyright (C) Microsoft Corporation. All rights reserved.

16.6.0.32601%

dotnet msbuild -version
Microsoft (R) Build Engine version 16.7.0-preview-20360-03+188921e2f for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

16.7.0.36003% 

Using restore has no effect.

Steps to Reproduce

See description above. I am not sure if I can attempt to create a minimal project to reproduce.

Expected Behavior

Resolving classes defined Nuget packages

Actual Behavior

Not resolved

Logs

OmniSharp log

[info]: OmniSharp.Stdio.Host
        Starting OmniSharp on ubuntu 16.4 (x64)
[info]: OmniSharp.Services.DotNetCliService
        DotNetPath set to dotnet
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Located 1 MSBuild instance(s)
            1: StandAlone 16.8.0 - "/some-path/.vscode/extensions/ms-dotnettools.csharp-1.23.1/.omnisharp/1.37.0/omnisharp/.msbuild/Current/Bin"
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        MSBUILD_EXE_PATH environment variable set to '/some-path/.vscode/extensions/ms-dotnettools.csharp-1.23.1/.omnisharp/1.37.0/omnisharp/.msbuild/Current/Bin/MSBuild.exe'
[info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
        Registered MSBuild instance: StandAlone 16.8.0 - "/some-path/.vscode/extensions/ms-dotnettools.csharp-1.23.1/.omnisharp/1.37.0/omnisharp/.msbuild/Current/Bin"
            CscToolExe = csc.exe
            MSBuildToolsPath = /some-path/.vscode/extensions/ms-dotnettools.csharp-1.23.1/.omnisharp/1.37.0/omnisharp/.msbuild/Current/Bin
            CscToolPath = /some-path/.vscode/extensions/ms-dotnettools.csharp-1.23.1/.omnisharp/1.37.0/omnisharp/.msbuild/Current/Bin/Roslyn
            BypassFrameworkInstallChecks = true
            MSBuildExtensionsPath = /some-path/.vscode/extensions/ms-dotnettools.csharp-1.23.1/.omnisharp/1.37.0/omnisharp/.msbuild
[info]: OmniSharp.Cake.CakeProjectSystem
        Detecting Cake files in '/some-path/private/some-project'.
[info]: OmniSharp.Cake.CakeProjectSystem
        Could not find any Cake files
[info]: OmniSharp.MSBuild.ProjectSystem
        Detecting projects in '/some-path/private/some-project/some-project.sln'.
[info]: OmniSharp.MSBuild.ProjectManager
        Queue project update for '/some-path/private/some-project/some-project.csproj'
[info]: OmniSharp.Script.ScriptProjectSystem
        Detecting CSX files in '/some-path/private/some-project'.
[info]: OmniSharp.Script.ScriptProjectSystem
        Could not find any CSX files
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0
[info]: OmniSharp.MSBuild.ProjectManager
        Loading project: /some-path/private/some-project/some-project.csproj
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.RenameWorkspaceOptionsProvider, Order: 100
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.ImplementTypeWorkspaceOptionsProvider, Order: 110
[info]: OmniSharp.WorkspaceInitializer
        Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.BlockStructureWorkspaceOptionsProvider, Order: 140
[info]: OmniSharp.WorkspaceInitializer
        Configuration finished.
[info]: OmniSharp.Stdio.Host
        Omnisharp server running using Stdio at location '/some-path/private/some-project' on host 23164.
[info]: OmniSharp.MSBuild.ProjectManager
        Successfully loaded project file '/some-path/private/some-project/some-project.csproj'.
[info]: OmniSharp.MSBuild.ProjectManager
        Adding project '/some-path/private/some-project/some-project.csproj'
[info]: OmniSharp.MSBuild.ProjectManager
        Update project: some-project

C# log

n/a

Environment information

VSCode version: 1.48.0
C# Extension: 1.23.1

Mono Information

OmniSharp using built-in mono

Dotnet Information

.NET Core SDK (reflecting any global.json): Version: 3.1.401 Commit: 39d17847db

Runtime Environment:
OS Name: ubuntu
OS Version: 16.04
OS Platform: Linux
RID: ubuntu.16.04-x64
Base Path: /usr/share/dotnet/sdk/3.1.401/

Host (useful for support):
Version: 3.1.7
Commit: fcfdef8d6b

.NET Core SDKs installed:
2.2.402 [/usr/share/dotnet/sdk]
3.1.401 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.2.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.2.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.7 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.2.8 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.7 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

Extension	Author	Version
cpptools	ms-vscode	0.29.0
csharp	ms-dotnettools	1.23.1
godot-tools	geequlim	1.1.1
mono-debug	ms-vscode	0.15.8
unity-debug	Unity	2.7.5
unity-tools	Tobiah	1.2.3
vscode-nuget-package-manager	jmrog	1.1.6
vscode-nxunit-test-adapter	wghats	0.1.3
vscode-test-explorer	hbenl	2.19.1

[nxfs]

Now that I read the release notice, I realize this is probably due to

Note about using .NET Core 3.1.401 or .NET 5 Preview 8 SDKs on Mono platforms

Because of the new minimum MSBuild version requirement of these new SDKs, it will be necessary to use the Mono packaged with the C# extension. You can set "omnisharp.useGlobalMono" to "never" in the VS Code settings to force the use of the included Mono.

I reverted the extension to 1.22 and it works. Is there any way I can keep using the latest version? Thanks for the help

[filipw]

thanks for the issue I will close it as a duplicate
see #4007 (comment) for a workaround