dotnet workload restore runtime jumps from 25 seconds to 4 minutes when nuget feed is AzDO instead of nuget.org

[AArnott]

Describe the bug

Frequent pipeline failures due to nuget.org not responding to package restore requests drives me to consider using a private Azure Artifacts feed instead of nuget.org in nuget.config.

But this change has an unexpected side-effect: the time to run dotnet workload restore jumps extremely:

Agent OS	nuget.org	AzDO feed	Time multiplier
Windows	30 s	80 s	2.6X
Linux	17 s	58 s	3.4X
macOS	25 s	244 s	9.7X

The macOS agent is the only one to display the following errors, which it does only after the change:

Installing workloads: 

Failed to update the advertising manifest microsoft.net.sdk.android: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.ios: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.maccatalyst: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.macos: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.maui: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.tvos: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.workload.mono.toolchain.current: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.workload.emscripten.current: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.workload.emscripten.net6: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.workload.emscripten.net7: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.workload.mono.toolchain.net6: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.workload.mono.toolchain.net7: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.aspire: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Failed to update the advertising manifest microsoft.net.sdk.android: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.sdk.android doesn't exist.
Failed to update the advertising manifest microsoft.net.sdk.ios: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.sdk.ios doesn't exist.
Failed to update the advertising manifest microsoft.net.sdk.maccatalyst: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.sdk.maccatalyst doesn't exist.
Failed to update the advertising manifest microsoft.net.sdk.macos: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.sdk.macos doesn't exist.
Failed to update the advertising manifest microsoft.net.sdk.maui: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.sdk.maui doesn't exist.
Failed to update the advertising manifest microsoft.net.sdk.tvos: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.sdk.tvos doesn't exist.
Failed to update the advertising manifest microsoft.net.workload.mono.toolchain.current: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.workload.mono.toolchain.current doesn't exist.
Failed to update the advertising manifest microsoft.net.workload.emscripten.current: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.workload.emscripten.current doesn't exist.
Failed to update the advertising manifest microsoft.net.workload.emscripten.net6: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.workload.emscripten.net6 doesn't exist.
Failed to update the advertising manifest microsoft.net.workload.emscripten.net7: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.workload.emscripten.net7 doesn't exist.
Failed to update the advertising manifest microsoft.net.workload.mono.toolchain.net6: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.workload.mono.toolchain.net6 doesn't exist.
Failed to update the advertising manifest microsoft.net.workload.mono.toolchain.net7: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..
Advertising manifest not updated. Manifest package for microsoft.net.workload.mono.toolchain.net7 doesn't exist.
Failed to update the advertising manifest microsoft.net.sdk.aspire: Unable to load the service index for source https://pkgs.dev.azure.com/andrewarnott/Git/_packaging/PrivateConsumption/nuget/v3/index.json..

Eventually the work completes (successfully I guess, because the rest of the build succeeds.)

This is repeatable. And the macOS agent has the authentication necessary to pull from the private feed.

Further technical details

 OS Platform: Darwin
 RID:         osx-arm64
 Base Path:   /Users/buildagent/myagent/_work/_tool/dotnet/sdk/8.0.400/

.NET workloads installed:
Configured to use loose manifests when installing new manifests.
 [ios]
   Installation Source: SDK 8.0.400
   Manifest Version:    18.0.8303/8.0.100
   Manifest Path:       /Users/buildagent/myagent/_work/_tool/dotnet/sdk-manifests/8.0.100/microsoft.net.sdk.ios/18.0.8303/WorkloadManifest.json
   Install Type:        FileBased


Host:
  Version:      8.0.8
  Architecture: arm64
  Commit:       08338fcaa5

.NET SDKs installed:
  8.0.300 [/Users/buildagent/myagent/_work/_tool/dotnet/sdk]
  8.0.400 [/Users/buildagent/myagent/_work/_tool/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.5 [/Users/buildagent/myagent/_work/_tool/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.8 [/Users/buildagent/myagent/_work/_tool/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 8.0.5 [/Users/buildagent/myagent/_work/_tool/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.6 [/Users/buildagent/myagent/_work/_tool/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.7 [/Users/buildagent/myagent/_work/_tool/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.8 [/Users/buildagent/myagent/_work/_tool/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  DOTNET_ROOT       [/Users/buildagent/myagent/_work/_tool/dotnet]