• This issue is blocking
  This is blocking any changes to the tasks in the release/3.x branch. So far it's blocking [Arcade v1] Remove stable version restriction from non-isolated feeds #5487
• This issue is causing unreasonable pain

While working on #5487 I had to produce a new version of Microsoft.DotNet.Build.Tasks.Feed and update arcade's 3.x branch to use that new version.

That new version of the task is causing publishing errors in repos subscribed to 3.x arcade, but using a newer version of the .net SDK.

Success Build using the minimum sdk that arcade 3.x enforces (3.0.101): https://dnceng.visualstudio.com/internal/_build/results?buildId=765409&view=results
Failure Build using latest released sdk (3.1.302): https://dnceng.visualstudio.com/internal/_build/results?buildId=765409&view=results
Failure Using a 3.1.4 preview (3.1.400-preview-015208): https://dnceng.visualstudio.com/internal/_build/results?buildId=759327&view=results

The error in the builds that fail to publish is:

\microsoft.dotnet.arcade.sdk\1.0.0-beta.20405.7\tools\SdkTasks\PublishArtifactsInManifest.proj(65,5): error : Method not found: 'System.Threading.Tasks.Task`1<Boolean> Sleet.PackageIndexFile.Exists(NuGet.Packaging.Core.PackageIdentity)'.

I'll revert the latest version upgrade, and sticking this in FR for investigation on how to unblock.