Team Visual Studio Services: build error (build link could not be resolved)

I am trying to create a project in Visual Studio Team Services that only builds locally and receives the following exceptions:

Code Analysis detected errors.  See Code Analysis results window or log file for details.
CA0001 : The following error was encountered while reading module 'Acme.Web': Assembly reference cannot be resolved: Microsoft.Owin, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35.
CA0058 : The referenced assembly 'Microsoft.Owin, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' could not be found. This assembly is required for analysis and was referenced by: C:\a\bin\Acme.Web.dll.

I looked through all the .csproj files and NuGet package files manually and did not find any links to Microsoft.Owin (2.0.0.0) - all projects seem to be referencing the correct build 2.1.0.0.

Does anyone have a hint where I could continue the search, or has anyone experienced a similar problem with VS Team Services CI?