VS2017 Found Conflicts between different versions of "System.Runtime" that could not be resolved

Question

I had a Visual Studio 2015 solution with 3 projects and then started using VS 2017 adding 2 new xunit projects. When I build everything succeeds but the tests are being discovered in Test Explorer.

I reviewed this question Found conflicts between different versions of the same dependent assembly that could not be resolved and set my Build output to Diagnostic and I am getting a warning saying:

1>  C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\Microsoft.Common.CurrentVersion.targets(2052,5): warning MSB3277: Found conflicts between different versions of "System.Runtime" that could not be resolved.  These reference conflicts are listed in the build log when log verbosity is set to detailed.

• i have updated the 3 .csproj files from Project ToolsVersion="14.0"to Project ToolsVersion="15.0"

• added <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects> to the 2 VS2017 projects which did not have it

• set Test -> Test Settings -> Default Processor Architecture to x64 and my Build -> Configuration Manager -> Platform to x64 or Any CPU (some projects do not allow x64?)

• I have reinstall nuget packages across the solutions with Update-Package -reinstall

• updated and repaired VS2017

I can see my tests on solution load but once I build the solution the tests are grayed out. Then I tried to run one and they say

4/4/2018 4:34:25 PM Warning] Test run will use DLL(s) built for framework Framework45 and platform X86. Following DLL(s) will not be part of run: 
DatabaseRestoreManager.exe, RestoreBaseLib.IntegrationTests.dll, RestoreBaseLib.Tests.dll, RestoreBaseLib.dll, Restores.exe are built for Framework Framework45 and Platform X64.
 Go to http://go.microsoft.com/fwlink/?LinkID=236877&clcid=0x409 for more details on managing these settings.
[4/4/2018 4:34:26 PM Warning] [xUnit.net 00:00:00.1993869] Exception discovering tests from RestoreBaseLib.IntegrationTests: System.BadImageFormatException: Could not load file or assembly 'RestoreBaseLib.IntegrationTests, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format.
File name: 'RestoreBaseLib.IntegrationTests, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'

Most people with this issue seem to have the problem in a nuget package but my issue seem to be a msbuild or VS15 to VS17 upgrade with testing and System.Runtime.

Is there anything that can fix this? I want to be able to run xunit tests in VS17.