I'm really new to this community. I'm sorry for any mistakes in advance.I'm making a game like minecraft with GLFW and OpenGL. The problem is, it just renders two faces correctly and the other faces have a wierd glitch. Here is my code:

main.py

#################################################################
#  ______   __  __   ______   ______     __     ______   ______ *
# |  __  |  \ \/ /  |  ____| |  __  |   /__\   /  ____| |__  __|*
# | |__| |   \  /   | |      | |__| |  //__\\ | |__       |  |  *
# |  ____|    ||    | |      |______| / ____ \|  __|      |  |  *
# | |         ||    | |____  | |\ \  / /    \ | |         |  |  *
# |_|         ||    |______| |_| \_\/_/      \|_|         |__|  *
#################################################################


# imports
import glfw
from OpenGL.GL import *
from OpenGL.GLU import *

# internal imports
from core.renderer import *
from player import *

if not glfw.init():
    raise Exception("glfw can not be initialized!")

window = glfw.create_window(800, 500, "PyCraft", None, None)
glfw.make_context_current(window)
renderer = TerrainRenderer(window)
player = Player(window)

renderer.texture_manager.add_from_folder("assets/textures/block/")
renderer.texture_manager.save("atlas.png")
renderer.texture_manager.bind()

glEnable(GL_DEPTH_TEST)
glEnable(GL_CULL_FACE)
glCullFace(GL_BACK)
glEnable(GL_FOG)
glFogfv(GL_FOG_COLOR, (GLfloat * int(8))(0.5, 0.69, 1.0, 10))
glHint(GL_FOG_HINT, GL_DONT_CARE)
glFogi(GL_FOG_MODE, GL_LINEAR)
glFogf(GL_FOG_START, 3)
glFogf(GL_FOG_END, 10)

# get window size
def get_window_size():
    width, height = glfw.get_window_size(window)
    return width, height

def _setup_3d():
    w, h = get_window_size()

    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    gluPerspective(70, w / h, 0.1, 1000)
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()

def _update_3d():
    _setup_3d()
    glViewport(0, 0, *get_window_size())

def add_cube(x, y, z):
    X, Y, Z = x + 1, y + 1, z + 1
    renderer.add((x, Y, Z,  X, Y, Z,  X, Y, z,  x, Y, z), renderer.texture_manager.get_texture("grass"))
    renderer.add((x, y, z, X, y, z, X, y, Z, x, y, Z), renderer.texture_manager.get_texture("grass"))
    renderer.add((x, y, z,  x, y, Z,  x, Y, Z,  x, Y, z), renderer.texture_manager.get_texture("grass"))
    renderer.add((X, y, Z,  X, y, z,  X, Y, z,  X, Y, Z), renderer.texture_manager.get_texture("grass"))
    renderer.add((x, y, Z,  X, y, Z,  X, Y, Z,  x, Y, Z), renderer.texture_manager.get_texture("grass"))
    renderer.add((X, y, z,  x, y, z,  x, Y, z,  X, Y, z), renderer.texture_manager.get_texture("grass"))

add_cube(0, 0, -2)

# mainloop
while not glfw.window_should_close(window):
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    _update_3d()
    glClearColor(0.5, 0.7, 1, 1.0)

    player.update()
    renderer.render()

    glfw.poll_events()
    glfw.swap_buffers(window)

glfw.terminate()

renderer.py:

#################################################################
#  ______   __  __   ______   ______     __     ______   ______ *
# |  __  |  \ \/ /  |  ____| |  __  |   /__\   /  ____| |__  __|*
# | |__| |   \  /   | |      | |__| |  //__\\ | |__       |  |  *
# |  ____|    ||    | |      |______| / ____ \|  __|      |  |  *
# | |         ||    | |____  | |\ \  / /    \ | |         |  |  *
# |_|         ||    |______| |_| \_\/_/      \|_|         |__|  *
#################################################################


# imports
import glfw
from OpenGL.GL import *
from OpenGL.GLU import *

# internal imports
from core.renderer import *
from player import *

if not glfw.init():
    raise Exception("glfw can not be initialized!")

window = glfw.create_window(800, 500, "PyCraft", None, None)
glfw.make_context_current(window)
renderer = TerrainRenderer(window)
player = Player(window)

renderer.texture_manager.add_from_folder("assets/textures/block/")
renderer.texture_manager.save("atlas.png")
renderer.texture_manager.bind()

glEnable(GL_DEPTH_TEST)
glEnable(GL_CULL_FACE)
glCullFace(GL_BACK)
glEnable(GL_FOG)
glFogfv(GL_FOG_COLOR, (GLfloat * int(8))(0.5, 0.69, 1.0, 10))
glHint(GL_FOG_HINT, GL_DONT_CARE)
glFogi(GL_FOG_MODE, GL_LINEAR)
glFogf(GL_FOG_START, 3)
glFogf(GL_FOG_END, 10)

# get window size
def get_window_size():
    width, height = glfw.get_window_size(window)
    return width, height

def _setup_3d():
    w, h = get_window_size()

    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    gluPerspective(70, w / h, 0.1, 1000)
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()

def _update_3d():
    _setup_3d()
    glViewport(0, 0, *get_window_size())

def add_cube(x, y, z):
    X, Y, Z = x + 1, y + 1, z + 1
    renderer.add((x, Y, Z,  X, Y, Z,  X, Y, z,  x, Y, z), renderer.texture_manager.get_texture("grass"))
    renderer.add((x, y, z, X, y, z, X, y, Z, x, y, Z), renderer.texture_manager.get_texture("grass"))
    renderer.add((x, y, z,  x, y, Z,  x, Y, Z,  x, Y, z), renderer.texture_manager.get_texture("grass"))
    renderer.add((X, y, Z,  X, y, z,  X, Y, z,  X, Y, Z), renderer.texture_manager.get_texture("grass"))
    renderer.add((x, y, Z,  X, y, Z,  X, Y, Z,  x, Y, Z), renderer.texture_manager.get_texture("grass"))
    renderer.add((X, y, z,  x, y, z,  x, Y, z,  X, Y, z), renderer.texture_manager.get_texture("grass"))

add_cube(0, 0, -2)

# mainloop
while not glfw.window_should_close(window):
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
    _update_3d()
    glClearColor(0.5, 0.7, 1, 1.0)

    player.update()
    renderer.render()

    glfw.poll_events()
    glfw.swap_buffers(window)

glfw.terminate()

It is expected that all faces of the above cube are lime.

Right now, it shows no errors, but it does not render the cube properly. The attached GIF explains what I mean. Any help will be highly appreciated.