Unable to discover Ibeacon while ranging it

Hello community members.
We are developing an android application in which we first list all the proximity ibeacons. User then selects one of the beacons to get the approximate distance between the phone and the beacon. Though we are done with the listing. There is a problem in ranging mean the application is not detecting the ibeacon even if it is closed enough. we are using official estimote SDK throughout for the beacons operations. One strange thing we faced that once we start ranging for the selected ibeacon the application continue searching and when we turn off the Bluetooth and then turn on Bluetooth without closing the application the ibeacon get discovered. We treid a lot but didn’t unable to capture the issue where it is.
Any help would be appreciated.