.NET Core Unit Tests Throwing FileLoadException

I'm certain these tests were running fine before I upgraded .NET Core, but I can't figure out how they are broken or why.

I have three libraries that I have developed. We'll call them A, B, and C. B depends on A directly, and C depends on B and A directly. They are all multi-targeted as .NET Standard 1.1+ and .NET Framework 4.5 libraries.

Libraries A and B work perfectly fine. The unit tests for library B rely on A functioning correctly, as a transitive dependency of library B. The build still works and the tests (xUnit) run fine.

In library C, I consume A and B directly. Although C and its unit tests build just fine, they don't run correctly. The unit test project for C is laid out exactly the same as library B's.

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFrameworks>netcoreapp1.1;net452</TargetFrameworks>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
    <PackageReference Include="xunit" Version="2.2.0" />
    <PackageReference Include="xunit.runner.visualstudio" Version="2.2.0" />
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\C\C.csproj" />
  </ItemGroup>

  <ItemGroup>
    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
  </ItemGroup>

When running the unit tests (in Visual Studio, dotnet test, or Cake), all tests pass under the full framework. When the .NET Core unit tests run, those that rely on a helper method from B (which in turn uses A) throw an exception:

System.IO.FileLoadException: Could not load file or assembly 'A, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'. Could not find or load a specific file. (Exception from HRESULT: 0x80131621)

I've checked the obvious problems: the library exists on our internal NuGet feed, the version numbers match between B and C (there's only one version, so no assembly binding redirects either), and A and B are definitely .NET Standard libraries, so they will work under .NET Core 1.1. I'm at a total loss because the .NET Framework version of the tests runs just fine, and I'm quite certain I would have noticed my tests failing before now. Does anyone have any suggestions?

There is a bug in .NET Core 1.1 regarding assemblies that are referenced by file: https://github.com/dotnet/coreclr/issues/10037#issuecomment-285394031

Could that issue apply here?