Vuforia Mid Plane doesn't work properly ONLY with vuforia core. But works with Vuforia samples asset

I've found a problem today and am stil yet to find the exact problem.

Basically I've set up a new project and installed vuforia core (8.1.10) with unity 2019.1 and Vuforia Samples asset.
I've set up a new scene to test Mid Air functionalities with just the AR Camera, Mid Air Positioner, Mid Air Stage, a light and a cube inside Mid Air Stage for spawn. Basic scene.
It works ok, as expected.

Then I created a new project because I didn't want the bloated vuforia samples asset and only imported the Core. Created again the basic scene but it does not work as before. It only works the first time I point to a contrasty area and does not work on floor or door or mid air as before.

Then I tested everyhing again, created the two projects multiple times and tested everything dozens of times. Tried to replicate the project setting that the vuforia samples have to my empty scene (with only vuforia core) unsuccessfully.

My question is: what does vuforia samples changes about the mid air performance? I couldn't find it exactly what is was but I think it's a Vuforia bug.