BluetoothLeScanner sometimes doesn't find beacon

hello, I’ve created an android App, using your SDK. The app run correctly but I’ve a problem during monitoring: BluetoothLeScanner doesn’t always find the beacon.
I’ve tried to extend the backgroundScanPeriod but I have the same results.
Could you suggest me a way to ensure that for every scanning I found the beacon?

Thank you

What device are you testing with? Some Android devices are better at consistently detecting beacons, some tend to lose the beacons between scan cycles. What backgroundScanPeriod settings do you use?

Hi thanks for your answer. Now I’ve solved that problem, but I’ve found another problem while testing.
My app initially was working but after some hours I found this error on Log:

02-09 11:43:56.721 9157-9201/com.github.florent37.emmet.sample I/EstimoteSDK: com.estimote.sdk.BeaconManager.startRanging:419 Region already ranged but that’s OK: Region{identifier=ranged region, proximityUUID=b9407f30-f5f8-466e-aff9-25556b57fe6d, major=null, minor=null}
02-09 11:43:56.741 9157-9209/com.github.florent37.emmet.sample E/BluetoothLeScanner: Error state, mLeHandle: -1
02-09 11:43:56.741 9157-9209/com.github.florent37.emmet.sample E/BluetoothLeScanner: Error state, mLeHandle: -1
02-09 11:43:56.791 9157-9260/com.github.florent37.emmet.sample D/BluetoothLeScanner: onClientRegistered() - status=0 clientIf=6
02-09 11:43:56.811 9157-9157/com.github.florent37.emmet.sample E/EstimoteSDK: com.estimote.sdk.service.internal.LollipopBluetoothAdapter$1.onScanFailed:91 Unable to start BLE scanning. Error code -99

what does it depend on? How can I solve it?