Vuforia Unity works on webcam but not on HoloLens

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.

1. Create new Unity project
2. Switch to UWP target
3. Enable XR the player settings and set WMR SDK
4. Enable Vuforia
5. Create a ARCaemra and a ImageTarget in the scene
6. Set the Device Type set to Digital Eyewear and Device Config set to HoloLens
7. Check the following Capabilities in Player Settings > Publish [SettingsInternetClient] [WebCam]