Debugging Unity Android with Visual Studio 2017 (when already working with MonoDevelop)

I am debugging with Windows 10 Pro (1709 - 16299.192), Visual Studio 2017 (15.5.2), VSTU (3.5.0.2), Unity 2017.3.0p1 and using the Standard Assets Example Project.

If I set preferences to MonoDevelop and select Attach to Process then the AndroidPlayer process is visible and I can successfully attach and debug.

However I set preferences to Visual Studio 2017 and open the C# Project, then select Attach Unity Debugger, then it does not show the AndroidPlayer and therefore I can't attach.

I can switch between MonoDevelop and Visual Studio 2017 and MonoDevelop always lists the process and Visual Studio 2017 doesn't.

I've tried uninstalling VSTU and re-installing it but this hasn't fixed the problem. I've also tried entering the explicit IP address MonoDevelop references when it's working

I can debug the local Unity Editor process from VS2017 with no problems.

Any suggestions of how to fix it or debug what is happening? Could it be a firewall setting?

Thanks

Jules