I first noticed this with the Hex Casting scrying lens, but it seems to happen with any trinket and any slot.
When you equip a trinket in creative mode, it first shows up in the other trinket slots that you're already hovering.

Then if you click in other trinket/armour slots, it starts showing up in other places.

Mod version: 3.3.1

I also got this crash once by putting the lens in the face slot and then right clicking the shield slot with a stack of items, but I can't reproduce it now: https://crashy.net/ic8sZIhdVYjNzNXI0981

This is in a moderately large modpack. I haven't tested just Trinkets and Hex alone. I can post the modlist if needed.

i have also had this issue occur

this is also an issue on 1.19.2 with the latest version of trinkets at the time of this message. I have trinkets, wizards, paladins and priests, backslot, backslot addon, artifacts and all of their dependencies installed. In this case I see it duplicate to one other slot at a time, but I also have a modpack where it fills every trinket slot in the inventory. In both cases this only occurs in creative mode, but causes a crash when it tries to fill the spell book slot from spell engine (wizards/paladins and priests dependency)

Confirm on 1.21 with origin wiki example and it releat to #273