While debugging a Xamarin Forms project on an iOS device, I will intermittently encounter "Please select a valid device before running the application". When this happens the Visual Studio 2017 IDE will show an active (green) "Paired to Mac - MacBook Air (connected)" is displayed. I can stop and restart Visual Studio and everything is fine ... for about 10 ~ 30 minutes. I have only one instance of Visual Studio running at any given time, and no one else shares this Mac. I have even rebuild my Windows 10 Pro machine as good measure. Rebooting the Mac does not seem to help either.
[MAC]
macOS Mojave 10.14.4
Xcode 10.2.1 (10E1001) April 17. 2019
[PC]
Windows 10 Pro Version 1809 OS Build 17763.437
Visual Studio 2017 Version 15.9.11
Xamarin 4.21.3.83
Xamarin.Designer 4.16.30
Xamarin.Templates 1.1.128
Xamarin.Android SDK 9.17.0
Xamarin.iOS and Xamarin.Mac SDK 12.4.0.64
.NET Framework Version 4.7.03190
Any ideas?