I noticed that when a shulker box in your hotbar has another shulker box to its left in the hotbar, it creates a very odd texture of jumbled block textures, which I have never seen before. I think this is kind of cool, but also distracting and might need to be fixed. Thanks!
P.S. This effect does not only happen when you are in the inventory screen, I just wanted to show off the difference between the expected texture and the ones I saw.
This may be caused by the resource pack you are using. Try disabling that and see if that fixes it