I have same problem with this…
Version: UE 4.20
Phone: Acer Liquid Z630
Android: 5.1 Lollipop
Laptop OS: Windows 10
I have followed all steps on the doc of unreal engine but still not working.
I have installed Android studio and my device was seen and working there… i tested my device on android studio and its working fine… but on unreal engine i cannot even see my device.
i checked it on adb and it was listed.
Please someone help/…