Intermittent "Unable to connect to a test backend" iOS Simulator

I have a bunch of tests which are running fine about 60% of the time, but other times they will simply fail with the the "Unable to connect to a test backed running app" exception. Now, because this is not happening on every single run, I don't think this is a setup/configuration issue.

• ENABLE_TEST_CLOUD symbol is set for the Debug configuration of the iOS app

• Xamarin.Calabash.Start() is called in AppDelegate.cs

• The Unit Tests pad/Test Apps link has been created to the iOS app
• XCode 8.1
• iOS 10.1 running in the iOS Simulator
• Xamarin.UITest v2.0.1
• Xamarin.TestCloud.Agent v0.20.3
• Xamarin Studio 6.1.2 build 44 (Beta channel)

Again, tests might run just fine on first run, and fail on second. A try...catch block wrapping the StartApp() call shows that the exception is (of course) raised there.

Any kind of help appreciated, thanks.