Not getting list of Android device


I am not getting a list of Android device under drop down, can anyone please help.
After click Ok it give blank list under device name.

But i am able to see list of IOS devices this problem is only with Android device list. Pls help to get this fixed.

Screen Shot 2018-02-20 at 2.47.39 PM.png

Screen Shot 2018-02-20 at 2.47.50 PM.png