Teensy LC Joypad not working in game

[TheMervinator]

Hey guys,
I've been having some confusing issues with a customer Teensy LC based controller that I made.
The controller is detected by Retropie and Emulation station perfectly well. The auto Config when first loading Emulation Station ran and generated the configuration files. It's works fine within Emulation station.

However, when starting any retroarch emulator, though it loads the configuration (according to the yellow text) the controls do not work. Special functions by pressing Select and any button work, to exit the emulator, or start the RGUI. But actual controls do not.
The Config generated:/opt/retropie/configs/all/retroarch-joypads/TeensyduinoTeensyFlightSimControls.cfg

input_device = "Teensyduino Teensy Flight Sim Controls"
input_driver = "udev"
input_r_y_plus_axis = "-2"
input_l3_btn = "5"
input_r_x_minus_axis = "-3"
input_l_btn = "12"
input_load_state_btn = "12"
input_start_btn = "15"
input_exit_emulator_btn = "15"
input_l_y_minus_axis = "-1"
input_up_btn = "6"
input_r_y_minus_axis = "+2"
input_a_btn = "4"
input_b_btn = "2"
input_reset_btn = "2"
input_down_btn = "8"
input_l_x_plus_axis = "+0"
input_l_y_plus_axis = "+1"
input_r_btn = "10"
input_save_state_btn = "10"
input_r2_btn = "11"
input_r3_btn = "0"
input_right_btn = "7"
input_state_slot_increase_btn = "7"
input_x_btn = "3"
input_menu_toggle_btn = "3"
input_select_btn = "14"
input_enable_hotkey_btn = "14"
input_l_x_minus_axis = "-0"
input_y_btn = "1"
input_left_btn = "9"
input_state_slot_decrease_btn = "9"
input_r_x_plus_axis = "+3"
input_l2_btn = "13"

Checking using jstest /dev/input/js0, the values appear correct. I've attempted to change the input_driver to SDL2 and linuxraw, in both this config and the configs/all/retroarch.cfg files, but neither these options work.

I'm at my wits end, because as I say, Retroarch appears configured correctly, and it accepts the 'special' inputs like SELECT+START to quit, but pressing start alone does nothing. Any help would be appreciated
Setup:
Pi 3 Model B, powered via the official RPi 3A power supply
Retropie 4.1
Built from Premade image on Retropie Website, fresh install
Teensy LC
Tested on the lr_MGBA and lr_picodrive emulators
Code running on Teensy: Pastebin

I greatly appreciate any assistance offered

[A Former User]

@TheMervinator I'm having the same issue did you ever find a solution?