Build failure: [release/uwp6.0] Failed to retrieve information about 'Microsoft.NET.Test.Sdk' #2908

error : Failed to retrieve information about 'Microsoft.NET.Test.Sdk' from remote source '/Users/buildagent/agent/_work/125/s/core-setup/Bin/osx-x64.Release/packages'. [/Users/buildagent/agent/_work/125/s/core-setup/src/test/HostActivationTests/HostActivationTests.csproj] [/Users/buildagent/agent/_work/125/s/core-setup/src/test/dir.proj]

/Users/buildagent/agent/_work/125/s/core-setup/src/test/dir.proj(62,5): error MSB3073: The command "DOTNET_SKIP_FIRST_TIME_EXPERIENCE=1 /Users/buildagent/agent/_work/125/s/core-setup/Tools/dotnetcli/dotnet restore --disable-parallel --packages "/Users/buildagent/agent/_work/125/s/core-setup/packages" --source https://dotnet.myget.org/F/dotnet-core/api/v3/index.json --source https://dotnet.myget.org/F/cli-deps/api/v3/index.json --source https://dotnet.myget.org/F/dotnet-buildtools/api/v3/index.json --source https://www.myget.org/F/nugetbuild/api/v3/index.json --source https://api.nuget.org/v3/index.json --source https://dotnet.myget.org/F/dotnet-corefxlab/api/v3/index.json --source /Users/buildagent/agent/_work/125/s/core-setup/Bin/osx-x64.Release/corehost --source /Users/buildagent/agent/_work/125/s/core-setup/Bin/osx-x64.Release/packages /p:MNAVersion=2.1.0 /p:TestTargetRid=osx-x64 /Users/buildagent/agent/_work/125/s/core-setup/src/test/HostActivationTests/HostActivationTests.csproj" exited with code 1.