I'm having a lot of trouble detecting beacon on SM-T280 (Android 5.1.1), the device recognize the beacons (Estimote) correctly but the RSSI value of beacons is pretty the same (-45 , -47) even if I'm using beacons meters away (One beacon close to the device and the other ~5mt, tried with different distance), so I cant estimate the nearest beacon. I've tried with different beacons and different devices (same model). All works well on other devices model. Could you please help me to understand why this happen?
Unfortunately it sounds like a hardware problem on the SM-T280. It's impossible to know why without troubleshooting the internal circuitry of the tablet. My conjecture is that the analog to digital converter on the signal output of the Bluetooth chip is somehow miswired or is otherwise malfunctioning. Without testing on several devices it is also impossible to know if this is a problem only on your unit, a certain percentage of these tablets or all of them.
Another less likely possibility is that this is a firmware problem with the bluetooth device driver that improperly scales the RSSI sensor output. If true, a different firmware version might fix the problem. You may want to see if any alternate Android ROMs are available for the device.