Updating to 1.20.5, models shading issue

I used a resource pack in 1.20.5, and the custom GUI models act weirdly, they are darker than they should, I think it's because it's shaded (because on the ground or in hand it is normal), but I don't know where it comes from. Everything works in 1.20.4 but not anymore in 1.20.5. Every other model (including the GUI buttons) render as usual. Can you help me ?