Nuget Feed publish failing

I have been successfully publishing a nuget package to the internal Team City nuget feed up until a few days ago when errors exactly like the below example started showing in the diagnostic logs. 

[2017-09-06 09:50:23,338]   INFO - NuGetArtifactsMetadataProvider - Indexing NuGet package from artifact MyNugetPackage.1.2.0.nupkg of build #2 {build id=2649, buildTypeId=MyBuild} 
[2017-09-06 09:50:23,339]   WARN - l.NuGetPackageStructureVisitor - Failed to read content of NuGet package MyNugetPackage.1.2.0.nupkg 
[2017-09-06 09:50:23,339]   WARN - NuGetArtifactsMetadataProvider - Failed to resolve NuGet package Id, package ignored: Artifact[promotionId=2649, relativePath=MyNugetPackage.1.2.0.nupkg] 
[2017-09-06 09:50:23,339]   INFO - NuGetArtifactsMetadataProvider - Indexing NuGet package from artifact MyNugetPackage.1.1.0.nupkg of build #2 {build id=2649, buildTypeId=MyBuild} 
[2017-09-06 09:50:23,339]   WARN - l.NuGetPackageStructureVisitor - Failed to read content of NuGet package MyNugetPackage.1.1.0.nupkg 
[2017-09-06 09:50:23,341]   WARN - NuGetArtifactsMetadataProvider - Failed to resolve NuGet package Id, package ignored: Artifact[promotionId=2649, relativePath=MyNugetPackage.1.1.0.nupkg] 

The configuration is simply this:

Package the nuget with:

dotnet pack %system.teamcity.build.workingDir%\MyProject.csproj -o ..\build\packages /p:PackageVersion=%NugetVersion%

And then set the artifact paths for this build configuration:

build\packages\** =>

I have tried: 

1. Clearing the nuget cache on our Team City server

2. Clearing the buildsMetadata cache via the Admin settings.

3. Disabling and re-enabling the nuget feed in the Admin settings.

4. Deleting ALL history of the builds so that our feed packages have been all removed (no published nuget versions remain)

But the above errors still persist, and no published nuget is showing up in the feed anymore.

It might be worth noting that this is from a .NET Core 2.0 Solution and the csproj that is being packed is referencing .NET Standard 2.0 and .NET Framework 4.5.

How can I fix this?