Gamepad R2 button doesn't work

Controller: Xiaomi Mi Bluetooth Wireless Gamepad
R2 button of controller doesn't work in MCPE on different phones. (Ex: ASUS and Samsung)

Steps to Reproduce:

1. Enable bluetooth of phone.
2. Connect gamepad to phone thru bluetooth.
3. Launch MCPE.
4. Go to setting for gamepad.
5. R2 cannot be assigned to any action, the default action doesn't work neither.

Observed Results:

Enter game and try to hit R2 button, and there is nothing happened.

Expected Results:

By hitting R2 button, character should do the action according to the in-game setting of gamepad.

Screenshots/Videos:

Provide on request.

Notes: