While the gamepad is connected you can't even launch the game, if I connect it after launching the game it crashes, so it is not possible to play the game with a gamepad in the current build.

You're right, must of slipped my mind.
I'm currently using an Xbox One Gamepad, either using Xow or connecting it via USB the game has the same problem

Launch game through terminal and see the output.

The moment I connect the gamepad the terminal shows the followiing before closing immediately.

GAMEPAD: Enumerating 27
Joystick: Xbox One Wireless Controller, bustype = 3, vendor = 0x045e, product = 0x02ea, version = 769
looks like a joystick with guid : 030000005e040000ea02000001030000
Unable to find mapping for device "Xbox One Wireless Controller"
Joystick has button: 0x130
Joystick has button: 0x131
Joystick has button: 0x133
Joystick has button: 0x134
Joystick has button: 0x136
Joystick has button: 0x137
Joystick has button: 0x13a
Joystick has button: 0x13b
Joystick has button: 0x13c
Joystick has button: 0x13d
Joystick has button: 0x13e
Joystick has absolute axis: 0x00
Values = { 1643, -32768, 32767, 255, 4095 }
Joystick has absolute axis: 0x01
Values = { 1417, -32768, 32767, 255, 4095 }
Joystick has absolute axis: 0x02
Values = { 0, 0, 1023, 3, 63 }
Joystick has absolute axis: 0x03
Values = { 1193, -32768, 32767, 255, 4095 }
Joystick has absolute axis: 0x04
Values = { 191, -32768, 32767, 255, 4095 }
Joystick has absolute axis: 0x05
Values = { 0, 0, 1023, 3, 63 }
Joystick has hat 0
Values = { 0, -1, 1, 0, 0 }
Joystick : Re-read Axis 0 (0) val= 0
Joystick : Re-read Axis 1 (1) val= 0
Joystick : Re-read Axis 2 (2) val= -32768
Joystick : Re-read Axis 3 (3) val= 0
Joystick : Re-read Axis 4 (4) val= 0
Joystick : Re-read Axis 5 (5) val= -32768
SWITCH!!
./run.sh: line 3: 2924209 Segmentation fault (core dumped) ./Loop_Hero

OK so I don't know how they implemented the gamepad, all I can say is that it doesn't like the Xbox One controller...

Using Xow's (the Xbox One Dongle driver) compatibility mode to mimic an X360 Pad worked.

I've only had to use this fix 3 times (4 counting this one):
-Mother Russia Bleeds
-Shadow Tactics: Blades of the Shogun
-Monolith

i don't know how or why a game released so recently has problems detecting and Xbox one controller but at least it's possible to play it this way.