[1.16.5] Custom Player Model Rendering Issue

So I want to create a new pose for my player.

I have tried using the PlayerRenderEvent.Pre and Post.

But the player's body are rendered upside down just like the following picture.

here is my code 

@OnlyIn(Dist.CLIENT)
@SubscribeEvent
public static void onPreRender(RenderPlayerEvent.Pre e){
    PlayerEntity p = e.getPlayer();
    if(p.getHeldItemMainhand().getItem() instanceof Lance){
      	PlayerModel<AbstractClientPlayerEntity> model = e.getRenderer().getEntityModel();
        model.bipedBody.showModel = false;
    }
}

@OnlyIn(Dist.CLIENT)
@SubscribeEvent
public static void onPostRender(RenderPlayerEvent.Post e){
    PlayerEntity p = e.getPlayer();
    if(p.getHeldItemMainhand().getItem() instanceof Lance){
      	PlayerModel<AbstractClientPlayerEntity> model = e.getRenderer().getEntityModel();
        IVertexBuilder builder = e.getBuffers().getBuffer(RenderType.getEntitySolid(((AbstractClientPlayerEntity)e.getPlayer()).getLocationSkin()));
        int light = e.getRenderer().getRenderManager().getPackedLight(e.getPlayer(), e.getPartialRenderTick());
        MatrixStack stack = e.getMatrixStack();
        model.bipedBody.showModel = true;
        model.bipedBody.render(stack, builder,light,655360);
    }
}

You can see I even didn't rotate anything.

I also have tried stack.push() and stack.pop() but it didn't help at all.

Can anyone help?

Thank you.