Reproduction steps:
1) Download attached project - 1007047_externalkeyboard.zip
2) Build and run it on an Android device
3) Connect external keyboard to the device
4) Try hitting enter (return) key
-- Notice that UI text element stays "New Text"

Expected result:
Input.GetKey(KeyCode.Return) and Input.GetKeyDown(KeyCode.Return) from the "NewBehaviourScript.cs" should change this text, indicating that the key was pressed

Note:
Instead of Input.GetKey(KeyCode.Return), return key on a keyboard is mapped to (KeyCode)10

Reproduced with:
2018.2.0a1, 2018.1.0b9, 2017.3.1p2, 2017.2.2f1, 2017.1.3p2, 5.6.5p2, 5.5.6f1

Devices under testing:
Reproduced with:
Google Pixel 2, Android 8.1
Samsung Galaxy Note 8, Android 7.1
LG G3, Android 5.0