I'm developing a simple App with Unity and Vuforia. This app recognize an image and place a simple 3D sphere onto it. If i run it on my MacBook Pro webcam inside Unity (i'm using Bootcamp) and i put a printed picture in front of it everything work fine and the sphere is placed correctly over the image.
When i build and export the project on Visual Studio 2019 and then i build and run on my HoloLens i can't see nothing if i look at the printed image.
If i look at the console i see 2 relevant things: 0x778E2FE2 (KernelBase.dll) in AR_Test.exe: WinRT originate error - 0xC00DABE0 : 'No capture devices are available.'.
AR:ERROR: 2019-10-10 04:11:30: You must successfully set a mode with Device.setMode before retrieving RenderingPrimitives
UPDATE
After updating Unity to the latest version (2019.2.8f1) and tried the Vuforia Sample Unity the project run on my HoloLens and i can see the Vuforia Splash Screen and the UI but i still can't see the models when i look at the target pictures. I get this on console in Visual Studio 2019:
AR:ERROR: 2019-10-10 06:38:20: VideoBackgroundConfig with screen size of zero received, skipping config step
AR:ERROR: 2019-10-10 06:38:20: You must successfully set a mode with Device.setMode before retrieving RenderingPrimitives
I use the unity(2019.2.8f1) with vuforia(8.3.8) to create a Unity APP to reproduce your issue but everything worked as expected. I would recommend you don't use the asset store sample, not sure when it was last updated. Please follow the step by step guide below to troubleshoot.