After a half day of frustration and searching, I finally found the problem. It is being detected as a Joystick rather than a keyboard and the input is ignored. Here's the fix:
Make a file under /storage/.config/udev.rules.d/
named "51-these-are-not-joysticks-rm.rules"
contents of file:
SUBSYSTEM=="input", ATTRS{idVendor}=="1d57", ATTRS{idProduct}=="ad03", ENV{ID_INPUT_JOYSTICK}=="?*", ENV{ID_INPUT_JOYSTICK}=""
SUBSYSTEM=="input", ATTRS{idVendor}=="1d57", ATTRS{idProduct}=="ad03", KERNEL=="js[0-9]*", MODE="0000", ENV{ID_INPUT_JOYSTICK}=""
Original post where I found this info:
[SOLVED] My RF remote has stopped working after migration to Kodi v17 - Raspberry Pi - OSMC Forums