C# 在.Net Core 3.1安装后，基于.Net 2.2的构建失败；无法加载文件或程序集NuGet.ProjectModel“； 构建突然开始失败

我们的解决方案包含针对.Net标准2.0、.Net核心2.2和.Net框架4.5的项目。很好的搭配。它是用

dotnet-c版本MyProject.sln构建的

有一天，我们开始遭受以下错误，但仅在我们的一个构建奴隶身上：

C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018: The "ResolvePackageAssets" task failed unexpectedly. [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018: System.IO.FileNotFoundException: Could not load file or assembly 'NuGet.ProjectModel, Version=5.4.0.2, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. The system cannot find the file specified. [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018: File name: 'NuGet.ProjectModel, Version=5.4.0.2, Culture=neutral, PublicKeyToken=31bf3856ad364e35' [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.CacheReader.CreateReaderFromMemory(ResolvePackageAssets task, Byte[] settingsHash) [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.CacheReader..ctor(ResolvePackageAssets task) [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ReadItemGroups() [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.NET.Build.Tasks.ResolvePackageAssets.ExecuteCore() [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.NET.Build.Tasks.TaskBase.Execute() [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:    at Microsoft.Build.BackEnd.TaskBuilder.ExecuteInstantiatedTask(ITaskExecutionHost taskExecutionHost, TaskLoggingContext taskLoggingContext, TaskHost taskHost, ItemBucket bucket, TaskExecutionMode howToExecuteTask) [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:  [D:\MyProject\MyProject.csproj]
C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets(234,5): error MSB4018:  [D:\MyProject\MyProject.csproj]

过去，在从机上安装.Net Core 3.1之后，我们遇到了一些问题，但在
global.json
中指向
2.2.100
解决了这些问题

现在，我们已尝试解决在多个源中搜索
无法加载文件或程序集的NuGet.ProjectModel…
和类似内容的新问题，尝试了许多不同的解决方案和解决方法，更新和修复了.Net Core和Visual Studio构建工具。不走运。
最后，我们在
dotnet build-c Release MyProject.sln-v diag的输出中发现了一些奇怪的东西：

MSBuildSDKsPath=C:\Program Files\dotnet\sdk\3.1.101\Sdks\
MSBuildToolsPath=C:\Program Files\dotnet\sdk\2.2.110

事实证明，我们已经在系统中设置了
MSBuildSDKsPath
变量并指向SDK，这打破了SDK降级的
global.json
。不知道，如果这是我的一些同事手动设置的，或者是在安装“某物”的过程中设置的，但它就在那里，占用了我2天的时间：-）