Proximity does not work in Xamarin Android App

Entry and Exit functions are not being triggered at my Xamarin Android App. I build my App following GitHub and Forum samples. The ProximityObserverBuilder and ProximityZoneBuilder, both work well (with no-errors). Bluetooth and Location permission passed ok the validation. I’m using two different Estimote stones (Ice and Mint). Both responses correctly when the Estimote Configuration app calls them. … everything seems to be correct. But, onEnter and onExit functions are not working. Nothing happens.

Any advice?
I’m using Android 7.1.2 phone with BLE support.